diff --git a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/AccelerationMode.java b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/AccelerationMode.java
index 836d32eab..bc0035a99 100644
--- a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/AccelerationMode.java
+++ b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/AccelerationMode.java
@@ -1,11 +1,24 @@
 package jp.hiroshiba.voicevoxcore;
 
 /** ハードウェアアクセラレーションモード。 */
-public enum AccelerationMode {
+public class AccelerationMode {
   /** 実行環境に合わせて自動的に選択する。 */
-  AUTO,
+  public static final AccelerationMode AUTO = new AccelerationMode("AUTO");
+
   /** CPUに設定する。 */
-  CPU,
+  public static final AccelerationMode CPU = new AccelerationMode("CPU");
+
   /** GPUに設定する。 */
-  GPU,
+  public static final AccelerationMode GPU = new AccelerationMode("GPU");
+
+  private final String identifier;
+
+  private AccelerationMode(String identifier) {
+    this.identifier = identifier;
+  }
+
+  @Override
+  public String toString() {
+    return identifier;
+  }
 }
diff --git a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/StyleType.java b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/StyleType.java
index e0eb699fb..b70bf0e82 100644
--- a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/StyleType.java
+++ b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/StyleType.java
@@ -1,27 +1,67 @@
 package jp.hiroshiba.voicevoxcore;
 
-import com.google.gson.annotations.Expose;
-import com.google.gson.annotations.SerializedName;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonParseException;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.JsonSerializationContext;
+import com.google.gson.JsonSerializer;
+import java.lang.reflect.Type;
 
 /** スタイル（style）に対応するモデルの種類。 */
-public enum StyleType {
+public class StyleType {
   /** 音声合成クエリの作成と音声合成が可能。 */
-  @SerializedName("talk")
-  @Expose
-  TALK,
+  public static final StyleType TALK = new StyleType("talk");
 
   /** 歌唱音声合成用のクエリの作成が可能。 */
-  @SerializedName("singing_teacher")
-  @Expose
-  SINGING_TEACHER,
+  public static final StyleType SINGING_TEACHER = new StyleType("singing_teacher");
 
   /** 歌唱音声合成が可能。 */
-  @SerializedName("frame_decode")
-  @Expose
-  FRAME_DECODE,
+  public static final StyleType FRAME_DECODE = new StyleType("frame_decode");
 
   /** 歌唱音声合成用のクエリの作成と歌唱音声合成が可能。 */
-  @SerializedName("sing")
-  @Expose
-  SING,
+  public static final StyleType SING = new StyleType("sing");
+
+  public static final class Serializer implements JsonSerializer<StyleType> {
+    @Override
+    public JsonElement serialize(StyleType src, Type typeOfSrc, JsonSerializationContext context) {
+      return new JsonPrimitive(src.toString());
+    }
+  }
+
+  public static final class Deserializer implements JsonDeserializer<StyleType> {
+    @Override
+    public StyleType deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
+        throws JsonParseException {
+      String value = json.getAsString();
+      switch (value) {
+        case "talk":
+          return TALK;
+        case "singing_teacher":
+          return SINGING_TEACHER;
+        case "frame_decode":
+          return FRAME_DECODE;
+        case "sing":
+          return SING;
+        default:
+          throw new JsonParseException(
+              String.format(
+                  "Invalid variant: `%s`, expected one of "
+                      + "`talk`, `singing_teacher`, `frame_decode`, `sing`",
+                  value));
+      }
+    }
+  }
+
+  private final String identifier;
+
+  private StyleType(String identifier) {
+    this.identifier = identifier;
+  }
+
+  @Override
+  public String toString() {
+    return identifier;
+  }
 }
diff --git a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/UserDictWord.java b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/UserDictWord.java
index 8b1e93457..f5ccfd3de 100644
--- a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/UserDictWord.java
+++ b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/UserDictWord.java
@@ -1,5 +1,12 @@
 package jp.hiroshiba.voicevoxcore;
 
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonParseException;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.JsonSerializationContext;
+import com.google.gson.JsonSerializer;
 import com.google.gson.annotations.Expose;
 import com.google.gson.annotations.SerializedName;
 import jakarta.annotation.Nonnull;
@@ -114,30 +121,66 @@ public UserDictWord priority(int priority) {
   private static native void rsValidatePronunciation(String pronunciation);
 
   /** 単語の種類。 */
-  public static enum Type {
+  public static class Type {
     /** 固有名詞。 */
-    @SerializedName("PROPER_NOUN")
-    @Expose
-    PROPER_NOUN,
+    public static final Type PROPER_NOUN = new Type("PROPER_NOUN");
 
     /** 一般名詞。 */
-    @SerializedName("COMMON_NOUN")
-    @Expose
-    COMMON_NOUN,
+    public static final Type COMMON_NOUN = new Type("COMMON_NOUN");
 
     /** 動詞。 */
-    @SerializedName("VERB")
-    @Expose
-    VERB,
+    public static final Type VERB = new Type("VERB");
 
     /** 形容詞。 */
-    @SerializedName("ADJECTIVE")
-    @Expose
-    ADJECTIVE,
+    public static final Type ADJECTIVE = new Type("ADJECTIVE");
 
     /** 語尾。 */
-    @SerializedName("SUFFIX")
-    @Expose
-    SUFFIX,
+    public static final Type SUFFIX = new Type("SUFFIX");
+
+    public static final class Serializer implements JsonSerializer<Type> {
+      @Override
+      public JsonElement serialize(
+          Type src, java.lang.reflect.Type typeOfSrc, JsonSerializationContext context) {
+        return new JsonPrimitive(src.toString());
+      }
+    }
+
+    public static final class Deserializer implements JsonDeserializer<Type> {
+      @Override
+      public Type deserialize(
+          JsonElement json, java.lang.reflect.Type typeOfT, JsonDeserializationContext context)
+          throws JsonParseException {
+        String value = json.getAsString();
+        switch (value) {
+          case "PROPER_NOUN":
+            return PROPER_NOUN;
+          case "COMMON_NOUN":
+            return COMMON_NOUN;
+          case "VERB":
+            return VERB;
+          case "ADJECTIVE":
+            return ADJECTIVE;
+          case "SUFFIX":
+            return SUFFIX;
+          default:
+            throw new JsonParseException(
+                String.format(
+                    "Invalid variant `%s`, expected one of "
+                        + "`PROPER_NOUN`, `COMMON_NOUN`, `VERB`, `ADJECTIVE`, `SUFFIX`",
+                    value));
+        }
+      }
+    }
+
+    private final String identifier;
+
+    private Type(String identifier) {
+      this.identifier = identifier;
+    }
+
+    @Override
+    public String toString() {
+      return identifier;
+    }
   }
 }
diff --git a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/Synthesizer.java b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/Synthesizer.java
index 8f5e9f49c..9cd385b98 100644
--- a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/Synthesizer.java
+++ b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/Synthesizer.java
@@ -1,6 +1,7 @@
 package jp.hiroshiba.voicevoxcore.blocking;
 
 import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
 import jakarta.annotation.Nonnull;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -11,6 +12,7 @@
 import jp.hiroshiba.voicevoxcore.AccentPhrase;
 import jp.hiroshiba.voicevoxcore.AudioQuery;
 import jp.hiroshiba.voicevoxcore.CharacterMeta;
+import jp.hiroshiba.voicevoxcore.StyleType;
 import jp.hiroshiba.voicevoxcore.exceptions.InvalidModelDataException;
 import jp.hiroshiba.voicevoxcore.exceptions.RunModelException;
 import jp.hiroshiba.voicevoxcore.internal.Dll;
@@ -64,7 +66,9 @@ public boolean isGpuMode() {
    */
   @Nonnull
   public CharacterMeta[] metas() {
-    Gson gson = new Gson();
+    GsonBuilder gsonBuilder = new GsonBuilder();
+    gsonBuilder.registerTypeAdapter(StyleType.class, new StyleType.Deserializer());
+    Gson gson = gsonBuilder.create();
     String metasJson = rsGetMetasJson();
     CharacterMeta[] rawMetas = gson.fromJson(metasJson, CharacterMeta[].class);
     if (rawMetas == null) {
diff --git a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/UserDict.java b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/UserDict.java
index e9819959a..1469a002e 100644
--- a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/UserDict.java
+++ b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/UserDict.java
@@ -1,6 +1,7 @@
 package jp.hiroshiba.voicevoxcore.blocking;
 
 import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
 import com.google.gson.internal.LinkedTreeMap;
 import jakarta.annotation.Nonnull;
 import java.io.File;
@@ -37,7 +38,9 @@ protected void finalize() throws Throwable {
    */
   @Nonnull
   public String addWord(UserDictWord word) {
-    Gson gson = new Gson();
+    GsonBuilder gsonBuilder = new GsonBuilder();
+    gsonBuilder.registerTypeAdapter(UserDictWord.Type.class, new UserDictWord.Type.Serializer());
+    Gson gson = gsonBuilder.create();
     String wordJson = gson.toJson(word);
 
     return rsAddWord(wordJson);
@@ -50,7 +53,9 @@ public String addWord(UserDictWord word) {
    * @param word 新しい単語のデータ。
    */
   public void updateWord(String uuid, UserDictWord word) {
-    Gson gson = new Gson();
+    GsonBuilder gsonBuilder = new GsonBuilder();
+    gsonBuilder.registerTypeAdapter(UserDictWord.Type.class, new UserDictWord.Type.Serializer());
+    Gson gson = gsonBuilder.create();
     String wordJson = gson.toJson(word);
 
     rsUpdateWord(uuid, wordJson);
@@ -142,7 +147,9 @@ public void save(String path) throws SaveUserDictException {
   @Nonnull
   public HashMap<String, UserDictWord> toHashMap() {
     String json = rsGetWords();
-    Gson gson = new Gson();
+    GsonBuilder gsonBuilder = new GsonBuilder();
+    gsonBuilder.registerTypeAdapter(UserDictWord.Type.class, new UserDictWord.Type.Deserializer());
+    Gson gson = gsonBuilder.create();
     @SuppressWarnings("unchecked")
     HashMap<String, LinkedTreeMap<String, ?>> rawWords = gson.fromJson(json, HashMap.class);
     if (rawWords == null) {
diff --git a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/VoiceModelFile.java b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/VoiceModelFile.java
index ebe6ac4ed..86e02425e 100644
--- a/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/VoiceModelFile.java
+++ b/crates/voicevox_core_java_api/lib/src/main/java/jp/hiroshiba/voicevoxcore/blocking/VoiceModelFile.java
@@ -1,10 +1,12 @@
 package jp.hiroshiba.voicevoxcore.blocking;
 
 import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
 import jakarta.annotation.Nonnull;
 import java.io.Closeable;
 import java.util.UUID;
 import jp.hiroshiba.voicevoxcore.CharacterMeta;
+import jp.hiroshiba.voicevoxcore.StyleType;
 import jp.hiroshiba.voicevoxcore.internal.Dll;
 
 /** 音声モデルファイル。 */
@@ -33,7 +35,9 @@ public VoiceModelFile(String modelPath) {
     rsOpen(modelPath);
     id = rsGetId();
     String metasJson = rsGetMetasJson();
-    Gson gson = new Gson();
+    GsonBuilder gsonBuilder = new GsonBuilder();
+    gsonBuilder.registerTypeAdapter(StyleType.class, new StyleType.Deserializer());
+    Gson gson = gsonBuilder.create();
     CharacterMeta[] rawMetas = gson.fromJson(metasJson, CharacterMeta[].class);
     if (rawMetas == null) {
       throw new RuntimeException("Failed to parse metasJson");
diff --git a/crates/voicevox_core_java_api/src/common.rs b/crates/voicevox_core_java_api/src/common.rs
index 22e10c2dc..65ce4ad3a 100644
--- a/crates/voicevox_core_java_api/src/common.rs
+++ b/crates/voicevox_core_java_api/src/common.rs
@@ -23,13 +23,13 @@ macro_rules! object_type {
     };
 }
 #[macro_export]
-macro_rules! enum_object {
-    ($env: ident, $name: literal, $variant: literal) => {
-        $env.get_static_field(object!($name), $variant, object_type!($name))
+macro_rules! static_field {
+    ($env: ident, $name: literal, $field: literal) => {
+        $env.get_static_field(object!($name), $field, object_type!($name))
             .unwrap_or_else(|_| {
                 panic!(
                     "Failed to get field {}",
-                    concat!($variant, "L", object!($name), ";")
+                    concat!($field, "L", object!($name), ";")
                 )
             })
             .l()
diff --git a/crates/voicevox_core_java_api/src/synthesizer.rs b/crates/voicevox_core_java_api/src/synthesizer.rs
index 2067d0c92..00318a3a2 100644
--- a/crates/voicevox_core_java_api/src/synthesizer.rs
+++ b/crates/voicevox_core_java_api/src/synthesizer.rs
@@ -1,6 +1,6 @@
 use crate::{
     common::{throw_if_err, JNIEnvExt as _, JavaApiError},
-    enum_object, object, object_type,
+    object, object_type, static_field,
 };
 
 use jni::{
@@ -31,9 +31,9 @@ unsafe extern "system" fn Java_jp_hiroshiba_voicevoxcore_blocking_Synthesizer_rs
         let acceleration_mode = if acceleration_mode.is_null() {
             Default::default()
         } else {
-            let auto = enum_object!(env, "AccelerationMode", "AUTO")?;
-            let cpu = enum_object!(env, "AccelerationMode", "CPU")?;
-            let gpu = enum_object!(env, "AccelerationMode", "GPU")?;
+            let auto = static_field!(env, "AccelerationMode", "AUTO")?;
+            let cpu = static_field!(env, "AccelerationMode", "CPU")?;
+            let gpu = static_field!(env, "AccelerationMode", "GPU")?;
             if env.is_same_object(&acceleration_mode, auto)? {
                 voicevox_core::AccelerationMode::Auto
             } else if env.is_same_object(&acceleration_mode, cpu)? {