diff --git a/src/converter/BUILD.bazel b/src/converter/BUILD.bazel
index a4fadb54d..040cbecd5 100644
--- a/src/converter/BUILD.bazel
+++ b/src/converter/BUILD.bazel
@@ -94,6 +94,7 @@ mozc_cc_test(
         ":segments",
         ":segments_matchers",
         "//testing:gunit_main",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
diff --git a/src/converter/segments_matchers_test.cc b/src/converter/segments_matchers_test.cc
index ac00237f0..9207fc04b 100644
--- a/src/converter/segments_matchers_test.cc
+++ b/src/converter/segments_matchers_test.cc
@@ -30,8 +30,8 @@
 #include "converter/segments_matchers.h"
 
 #include <string>
-#include <vector>
 
+#include "absl/types/span.h"
 #include "converter/segments.h"
 #include "testing/gmock.h"
 #include "testing/gunit.h"
@@ -55,7 +55,7 @@ Segment::Candidate MakeCandidate(const std::string &key,
 }
 
 Segment MakeSegment(const std::string &key,
-                    const std::vector<std::string> &values) {
+                    absl::Span<const std::string> values) {
   Segment seg;
   seg.set_key(key);
   for (const std::string &val : values) {
diff --git a/src/dictionary/BUILD.bazel b/src/dictionary/BUILD.bazel
index 53e88ce79..0155508b0 100644
--- a/src/dictionary/BUILD.bazel
+++ b/src/dictionary/BUILD.bazel
@@ -336,6 +336,7 @@ mozc_cc_test(
         "//testing:mozctest",
         "//testing:testing_util",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
diff --git a/src/dictionary/user_dictionary_session_handler_test.cc b/src/dictionary/user_dictionary_session_handler_test.cc
index 188e65556..f375015e0 100644
--- a/src/dictionary/user_dictionary_session_handler_test.cc
+++ b/src/dictionary/user_dictionary_session_handler_test.cc
@@ -36,6 +36,7 @@
 #include <vector>
 
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/file_util.h"
 #include "base/protobuf/repeated_ptr_field.h"
 #include "base/system_util.h"
@@ -154,7 +155,7 @@ class UserDictionarySessionHandlerTest
 
   RepeatedPtrField<UserDictionary::Entry> GetUserDictionaryEntries(
       uint64_t session_id, uint64_t dictionary_id,
-      const std::vector<int> &indices) {
+      absl::Span<const int> indices) {
     Clear();
     command_->set_type(UserDictionaryCommand::GET_ENTRIES);
     command_->set_session_id(session_id);
diff --git a/src/prediction/BUILD.bazel b/src/prediction/BUILD.bazel
index 1c956cafa..81d978b62 100644
--- a/src/prediction/BUILD.bazel
+++ b/src/prediction/BUILD.bazel
@@ -400,6 +400,7 @@ mozc_cc_test(
         "//request:request_test_util",
         "//testing:gunit_main",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
@@ -501,6 +502,7 @@ mozc_cc_binary(
         "@com_google_absl//absl/flags:flag",
         "@com_google_absl//absl/log",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
diff --git a/src/prediction/gen_suggestion_filter_main.cc b/src/prediction/gen_suggestion_filter_main.cc
index a99516b9a..207aaf687 100644
--- a/src/prediction/gen_suggestion_filter_main.cc
+++ b/src/prediction/gen_suggestion_filter_main.cc
@@ -37,6 +37,7 @@
 #include "absl/flags/flag.h"
 #include "absl/log/log.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/codegen_bytearray_stream.h"
 #include "base/file_stream.h"
 #include "base/hash.h"
@@ -91,19 +92,19 @@ void ReadSafeWords(const absl::string_view safe_list_files,
 constexpr size_t kMinimumFilterBytes = 100 * 1000;
 
 ExistenceFilterBuilder GetFilter(const size_t num_bytes,
-                                 const std::vector<uint64_t> &hash_list) {
+                                 absl::Span<const uint64_t> hash_list) {
   LOG(INFO) << "num_bytes: " << num_bytes;
 
   ExistenceFilterBuilder filter(
       ExistenceFilterBuilder::CreateOptimal(num_bytes, hash_list.size()));
-  for (size_t i = 0; i < hash_list.size(); ++i) {
-    filter.Insert(hash_list[i]);
+  for (uint64_t hash : hash_list) {
+    filter.Insert(hash);
   }
   return filter;
 }
 
 bool TestFilter(const ExistenceFilterBuilder &builder,
-                const std::vector<std::string> &safe_word_list) {
+                absl::Span<const std::string> safe_word_list) {
   ExistenceFilter filter = builder.Build();
   for (const std::string &word : safe_word_list) {
     if (filter.Exists(mozc::Fingerprint(word))) {
@@ -116,8 +117,8 @@ bool TestFilter(const ExistenceFilterBuilder &builder,
 }
 
 ExistenceFilterBuilder SetupFilter(
-    const size_t num_bytes, const std::vector<uint64_t> &hash_list,
-    const std::vector<std::string> &safe_word_list) {
+    const size_t num_bytes, absl::Span<const uint64_t> hash_list,
+    absl::Span<const std::string> safe_word_list) {
   constexpr int kNumRetryMax = 10;
   constexpr int kSizeOffset = 8;
   // Prevent filtering of common words by false positive.
diff --git a/src/prediction/single_kanji_prediction_aggregator_test.cc b/src/prediction/single_kanji_prediction_aggregator_test.cc
index 789d6c1c8..e9afa3748 100644
--- a/src/prediction/single_kanji_prediction_aggregator_test.cc
+++ b/src/prediction/single_kanji_prediction_aggregator_test.cc
@@ -33,6 +33,7 @@
 #include <vector>
 
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/strings/unicode.h"
 #include "composer/composer.h"
 #include "composer/table.h"
@@ -58,7 +59,7 @@ void SetUpInputWithKey(absl::string_view key, composer::Composer *composer,
   seg->set_segment_type(Segment::FREE);
 }
 
-bool FindResultByKey(const std::vector<Result> &results,
+bool FindResultByKey(absl::Span<const Result> results,
                      const absl::string_view key) {
   for (const auto &result : results) {
     if (result.key == key && !result.removed) {
diff --git a/src/rewriter/BUILD.bazel b/src/rewriter/BUILD.bazel
index 82060e0b3..2e863b45f 100644
--- a/src/rewriter/BUILD.bazel
+++ b/src/rewriter/BUILD.bazel
@@ -136,6 +136,7 @@ mozc_cc_library(
         "@com_google_absl//absl/log:check",
         "@com_google_absl//absl/status",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
     alwayslink = 1,
 )
@@ -391,6 +392,7 @@ mozc_cc_library(
         "@com_google_absl//absl/log",
         "@com_google_absl//absl/log:check",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
     alwayslink = 1,
 )
@@ -1006,6 +1008,7 @@ mozc_cc_library(
         "@com_google_absl//absl/log",
         "@com_google_absl//absl/log:check",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
     alwayslink = 1,
 )
@@ -1228,6 +1231,7 @@ mozc_cc_library(
         "@com_google_absl//absl/log",
         "@com_google_absl//absl/log:check",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
@@ -1250,6 +1254,7 @@ mozc_cc_test(
         "//testing:mozctest",
         "@com_google_absl//absl/container:btree",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
@@ -1293,6 +1298,7 @@ mozc_cc_binary(
         "@com_google_absl//absl/log",
         "@com_google_absl//absl/log:check",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
diff --git a/src/rewriter/environmental_filter_rewriter.cc b/src/rewriter/environmental_filter_rewriter.cc
index 57de4cc1b..ccb8ae240 100644
--- a/src/rewriter/environmental_filter_rewriter.cc
+++ b/src/rewriter/environmental_filter_rewriter.cc
@@ -44,6 +44,7 @@
 #include "absl/log/check.h"
 #include "absl/log/log.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/container/serialized_string_array.h"
 #include "base/text_normalizer.h"
 #include "base/util.h"
@@ -203,7 +204,7 @@ EmojiDataIterator end(const absl::string_view token_array_data) {
 
 absl::flat_hash_map<EmojiVersion, std::vector<std::u32string>>
 ExtractTargetEmojis(
-    const std::vector<EmojiVersion> &target_versions,
+    absl::Span<const EmojiVersion> target_versions,
     const std::pair<EmojiDataIterator, EmojiDataIterator> &range,
     const SerializedStringArray &string_array) {
   absl::flat_hash_map<EmojiVersion, std::vector<std::u32string>> results;
@@ -237,7 +238,7 @@ std::u32string SortAndUnique(std::u32string_view codepoints) {
 }  // namespace
 
 void CharacterGroupFinder::Initialize(
-    const std::vector<std::u32string> &target_codepoints) {
+    absl::Span<const std::u32string> target_codepoints) {
   std::u32string single_codepoints;
   for (const auto &codepoints : target_codepoints) {
     const size_t size = codepoints.size();
diff --git a/src/rewriter/environmental_filter_rewriter.h b/src/rewriter/environmental_filter_rewriter.h
index 74a1658f0..a47c8203f 100644
--- a/src/rewriter/environmental_filter_rewriter.h
+++ b/src/rewriter/environmental_filter_rewriter.h
@@ -56,6 +56,7 @@
 #include <string_view>
 #include <vector>
 
+#include "absl/types/span.h"
 #include "base/text_normalizer.h"
 #include "converter/segments.h"
 #include "data_manager/data_manager_interface.h"
@@ -70,7 +71,7 @@ class CharacterGroupFinder {
   ~CharacterGroupFinder() = default;
 
   // Sets target_codepoints, which represents target group.
-  void Initialize(const std::vector<std::u32string> &target_codepoints);
+  void Initialize(absl::Span<const std::u32string> target_codepoints);
   // Finds targeted character in given target codepoints. If found, returns
   // true. If not found, returns false.
   bool FindMatch(std::u32string_view target) const;
diff --git a/src/rewriter/environmental_filter_rewriter_test.cc b/src/rewriter/environmental_filter_rewriter_test.cc
index 13f69e8e0..201520af5 100644
--- a/src/rewriter/environmental_filter_rewriter_test.cc
+++ b/src/rewriter/environmental_filter_rewriter_test.cc
@@ -37,6 +37,7 @@
 
 #include "absl/container/btree_map.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/container/serialized_string_array.h"
 #include "base/text_normalizer.h"
 #include "base/util.h"
@@ -65,7 +66,7 @@ void AddSegment(const absl::string_view key, const absl::string_view value,
 }
 
 void AddSegment(const absl::string_view key,
-                const std::vector<std::string> &values, Segments *segments) {
+                absl::Span<const std::string> values, Segments *segments) {
   Segment *seg = segments->add_segment();
   seg->set_key(key);
   for (const std::string &value : values) {
diff --git a/src/rewriter/gen_usage_rewriter_dictionary_main.cc b/src/rewriter/gen_usage_rewriter_dictionary_main.cc
index 25c64e508..550780a7d 100644
--- a/src/rewriter/gen_usage_rewriter_dictionary_main.cc
+++ b/src/rewriter/gen_usage_rewriter_dictionary_main.cc
@@ -111,6 +111,7 @@
 #include "absl/strings/str_replace.h"
 #include "absl/strings/str_split.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/container/serialized_string_array.h"
 #include "base/file_stream.h"
 #include "base/init_mozc.h"
@@ -326,7 +327,7 @@ void Convert() {
                              std::ios_base::out | std::ios_base::binary);
     int out_count = 0;
     for (size_t i = 0; i < conjugation_list.size(); ++i) {
-      const std::vector<ConjugationType> &conjugations =
+      absl::Span<const ConjugationType> conjugations =
           inflection_map[conjugation_list[i]];
       conjugation_index[i] = out_count;
       if (conjugations.empty()) {
diff --git a/src/rewriter/single_kanji_rewriter.cc b/src/rewriter/single_kanji_rewriter.cc
index cdf068079..289cc41fe 100644
--- a/src/rewriter/single_kanji_rewriter.cc
+++ b/src/rewriter/single_kanji_rewriter.cc
@@ -38,6 +38,7 @@
 #include "absl/log/check.h"
 #include "absl/log/log.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/strings/assign.h"
 #include "base/vlog.h"
 #include "converter/segments.h"
@@ -200,7 +201,7 @@ void SingleKanjiRewriter::AddDescriptionForExistingCandidates(
 // Insert SingleKanji into segment.
 bool SingleKanjiRewriter::InsertCandidate(
     bool is_single_segment, uint16_t single_kanji_id,
-    const std::vector<std::string> &kanji_list, Segment *segment) const {
+    absl::Span<const std::string> kanji_list, Segment *segment) const {
   DCHECK(segment);
   DCHECK(!kanji_list.empty());
   if (segment->candidates_size() == 0) {
diff --git a/src/rewriter/single_kanji_rewriter.h b/src/rewriter/single_kanji_rewriter.h
index 6a2e40173..220a491c6 100644
--- a/src/rewriter/single_kanji_rewriter.h
+++ b/src/rewriter/single_kanji_rewriter.h
@@ -33,9 +33,9 @@
 #include <cstdint>
 #include <memory>
 #include <string>
-#include <vector>
 
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "converter/segments.h"
 #include "data_manager/data_manager_interface.h"
 #include "dictionary/pos_matcher.h"
@@ -58,7 +58,7 @@ class SingleKanjiRewriter : public RewriterInterface {
  private:
   void AddDescriptionForExistingCandidates(Segment *segment) const;
   bool InsertCandidate(bool is_single_segment, uint16_t single_kanji_id,
-                       const std::vector<std::string> &kanji_list,
+                       absl::Span<const std::string> kanji_list,
                        Segment *segment) const;
   void FillCandidate(absl::string_view key, absl::string_view value, int cost,
                      uint16_t single_kanji_id, Segment::Candidate *cand) const;
diff --git a/src/rewriter/transliteration_rewriter.cc b/src/rewriter/transliteration_rewriter.cc
index b23d69de1..208fb6fdb 100644
--- a/src/rewriter/transliteration_rewriter.cc
+++ b/src/rewriter/transliteration_rewriter.cc
@@ -39,6 +39,7 @@
 #include "absl/log/check.h"
 #include "absl/log/log.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/japanese_util.h"
 #include "base/number_util.h"
 #include "base/text_normalizer.h"
@@ -183,12 +184,12 @@ void ModifyT13nsForGodan(const absl::string_view key,
   (*t13ns)[transliteration::FULL_ASCII_CAPITALIZED] = full_ascii_capitalized;
 }
 
-bool IsTransliterated(const std::vector<std::string> &t13ns) {
+bool IsTransliterated(absl::Span<const std::string> t13ns) {
   if (t13ns.empty() || t13ns[0].empty()) {
     return false;
   }
 
-  const std::string &base_candidate = t13ns[0];
+  absl::string_view base_candidate = t13ns[0];
   for (size_t i = 1; i < t13ns.size(); ++i) {
     if (t13ns[i] != base_candidate) {
       return true;
@@ -433,7 +434,7 @@ void TransliterationRewriter::InitT13nCandidate(
 }
 
 bool TransliterationRewriter::SetTransliterations(
-    const std::vector<std::string> &t13ns, const absl::string_view key,
+    absl::Span<const std::string> t13ns, const absl::string_view key,
     Segment *segment) const {
   if (t13ns.size() != transliteration::NUM_T13N_TYPES ||
       !IsTransliterated(t13ns)) {
diff --git a/src/rewriter/transliteration_rewriter.h b/src/rewriter/transliteration_rewriter.h
index 19aa75cad..ebe3612c4 100644
--- a/src/rewriter/transliteration_rewriter.h
+++ b/src/rewriter/transliteration_rewriter.h
@@ -32,9 +32,9 @@
 
 #include <cstdint>
 #include <string>
-#include <vector>
 
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "converter/segments.h"
 #include "dictionary/pos_matcher.h"
 #include "request/conversion_request.h"
@@ -62,7 +62,7 @@ class TransliterationRewriter : public RewriterInterface {
                          Segment::Candidate *cand) const;
   // Sets transliteration values into segment.  If t13ns is invalid,
   // false is returned.
-  bool SetTransliterations(const std::vector<std::string> &t13ns,
+  bool SetTransliterations(absl::Span<const std::string> t13ns,
                            absl::string_view key, Segment *segment) const;
   bool FillT13nsFromComposer(const ConversionRequest &request,
                              Segments *segments) const;
diff --git a/src/rewriter/user_segment_history_rewriter.cc b/src/rewriter/user_segment_history_rewriter.cc
index 4833821cf..a7ab1eca5 100644
--- a/src/rewriter/user_segment_history_rewriter.cc
+++ b/src/rewriter/user_segment_history_rewriter.cc
@@ -46,6 +46,7 @@
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_join.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/config_file_stream.h"
 #include "base/file_util.h"
 #include "base/number_util.h"
@@ -403,7 +404,7 @@ bool IsT13NCandidate(const Segment::Candidate &cand) {
 }  // namespace
 
 bool UserSegmentHistoryRewriter::SortCandidates(
-    const std::vector<ScoreCandidate> &sorted_scores, Segment *segment) const {
+    absl::Span<const ScoreCandidate> sorted_scores, Segment *segment) const {
   const uint32_t top_score = sorted_scores[0].score;
   const size_t size = std::min(sorted_scores.size(), kMaxRerankSize);
   constexpr uint32_t kScoreGap = 20;  // TODO(taku): no justification
diff --git a/src/rewriter/user_segment_history_rewriter.h b/src/rewriter/user_segment_history_rewriter.h
index 2939c9ab9..8c22a3af4 100644
--- a/src/rewriter/user_segment_history_rewriter.h
+++ b/src/rewriter/user_segment_history_rewriter.h
@@ -34,9 +34,9 @@
 #include <cstddef>
 #include <cstdint>
 #include <memory>
-#include <vector>
 
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "converter/segments.h"
 #include "dictionary/pos_group.h"
 #include "dictionary/pos_matcher.h"
@@ -103,7 +103,7 @@ class UserSegmentHistoryRewriter : public RewriterInterface {
   void InsertTriggerKey(const Segment &segment);
   bool IsPunctuation(const Segment &seg,
                      const Segment::Candidate &candidate) const;
-  bool SortCandidates(const std::vector<ScoreCandidate> &sorted_scores,
+  bool SortCandidates(absl::Span<const ScoreCandidate> sorted_scores,
                       Segment *segment) const;
   Score Fetch(absl::string_view key, uint32_t weight) const;
   void Insert(absl::string_view key, bool force);
diff --git a/src/session/internal/BUILD.bazel b/src/session/internal/BUILD.bazel
index dc553836d..eeba49a33 100644
--- a/src/session/internal/BUILD.bazel
+++ b/src/session/internal/BUILD.bazel
@@ -125,6 +125,7 @@ mozc_cc_library(
         "@com_google_absl//absl/log",
         "@com_google_absl//absl/log:check",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/types:span",
     ],
 )
 
diff --git a/src/session/internal/session_output.cc b/src/session/internal/session_output.cc
index 477205600..e8ce7a019 100644
--- a/src/session/internal/session_output.cc
+++ b/src/session/internal/session_output.cc
@@ -43,6 +43,7 @@
 #include "absl/log/log.h"
 #include "absl/strings/str_split.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/span.h"
 #include "base/strings/assign.h"
 #include "base/text_normalizer.h"
 #include "base/util.h"
@@ -248,7 +249,7 @@ void SessionOutput::FillAllCandidateWords(
 void SessionOutput::FillRemovedCandidates(
     const Segment &segment, commands::CandidateList *candidate_list_proto) {
   int index = 1000;
-  const std::vector<Segment::Candidate> &candidates =
+  absl::Span<const Segment::Candidate> candidates =
       segment.removed_candidates_for_debug_;
   for (const Segment::Candidate &candidate : candidates) {
     commands::CandidateWord *candidate_word_proto =