diff --git a/.idea/compiler.xml b/.idea/compiler.xml
index b589d56..b86273d 100644
--- a/.idea/compiler.xml
+++ b/.idea/compiler.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="CompilerConfiguration">
-    <bytecodeTargetLevel target="17" />
+    <bytecodeTargetLevel target="21" />
   </component>
 </project>
\ No newline at end of file
diff --git a/.idea/deploymentTargetSelector.xml b/.idea/deploymentTargetSelector.xml
index 07cf77d..1b50529 100644
--- a/.idea/deploymentTargetSelector.xml
+++ b/.idea/deploymentTargetSelector.xml
@@ -4,10 +4,10 @@
     <selectionStates>
       <SelectionState runConfigName="app">
         <option name="selectionMode" value="DROPDOWN" />
-        <DropdownSelection timestamp="2025-12-18T07:06:50.954224800Z">
+        <DropdownSelection timestamp="2025-12-18T08:19:47.209540700Z">
           <Target type="DEFAULT_BOOT">
             <handle>
-              <DeviceId pluginId="LocalEmulator" identifier="path=C:\Users\natsu\.android\avd\Pixel_8.avd" />
+              <DeviceId pluginId="LocalEmulator" identifier="path=C:\Users\natsu\.android\avd\Pixel_7_2.avd" />
             </handle>
           </Target>
         </DropdownSelection>
diff --git a/.idea/misc.xml b/.idea/misc.xml
index 8978d23..74dd639 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -1,6 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="ExternalStorageConfigurationManager" enabled="true" />
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_17" default="true" project-jdk-name="jbr-17" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="jbr-21" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/build/classes" />
   </component>
   <component name="ProjectType">
diff --git a/app/src/main/java/com/example/tampopo_client/views/MainActivity.java b/app/src/main/java/com/example/tampopo_client/views/MainActivity.java
index 5bf8466..fcaa661 100644
--- a/app/src/main/java/com/example/tampopo_client/views/MainActivity.java
+++ b/app/src/main/java/com/example/tampopo_client/views/MainActivity.java
@@ -130,6 +130,30 @@
             public void onChanged(List<String> friends) {
                 // フレンドの追加と削除
                 updateActivityView(friends);
+                
+                // 各フレンドのアクティビティ更新を監視
+                for (String friendId : friends) {
+                    // 既にObserverが登録済みの場合はスキップ
+                    if (observedFriendIds.contains(friendId)) {
+                        continue;
+                    }
+                    
+                    MutableLiveData<List<Activity>> activitiesLiveData = activityViewModel.getActivitiesLiveDataFromUserId(friendId);
+                    activitiesLiveData.observe(MainActivity.this, activities -> {
+                        if (activities == null || activities.isEmpty()) return;
+
+                        Activity latest = activities.get(0);
+
+                        // UIスレッドで安全に更新
+                        FriendIconView friendView = userViews.get(friendId);
+                        if (friendView != null) {
+                            friendView.setComment(latest.getText());
+                            Log.d("ActivityUpdate", friendId + " のコメントを更新: " + latest.getText());
+                        }
+                    });
+                    // Observer登録済みとしてマーク
+                    observedFriendIds.add(friendId);
+                }
             }
         });
 
@@ -352,30 +376,9 @@
         i = 0;
         for (String friendId : friends) {
             FriendIconView userView = userViews.get(friendId);
-            MutableLiveData<List<Activity>> activitiesLiveData = activityViewModel.getActivitiesLiveDataFromUserId(friendId);
 
-            // 既存のフレンドの場合は、Observerを登録するだけ（Viewは作成しない）
+            // 既存のフレンドの場合はスキップ（Viewは既に作成済み、ObserverはonCreate()で登録済み）
             if (userView != null) {
-                // 既にObserverが登録済みの場合はスキップ
-                if (observedFriendIds.contains(friendId)) {
-                    continue;
-                }
-                
-                // 既にViewが存在する場合は、Observerだけを登録
-                activitiesLiveData.observe(MainActivity.this, activities -> {
-                    if (activities == null || activities.isEmpty()) return;
-
-                    Activity latest = activities.get(0);
-
-                    // UIスレッドで安全に更新
-                    FriendIconView friendView = userViews.get(friendId);
-                    if (friendView != null) {
-                        friendView.setComment(latest.getText());
-                        Log.d("ActivityUpdate", friendId + " のコメントを更新: " + latest.getText());
-                    }
-                });
-                // Observer登録済みとしてマーク
-                observedFriendIds.add(friendId);
                 continue;
             }
 
@@ -424,21 +427,7 @@
                                 i++;
                             }
 
-                            // 新規作成したViewに対してObserverを登録
-                            activitiesLiveData.observe(MainActivity.this, activities -> {
-                                if (activities == null || activities.isEmpty()) return;
-
-                                Activity latest = activities.get(0);
-
-                                // UIスレッドで安全に更新
-                                FriendIconView friendView = userViews.get(friendId);
-                                if (friendView != null) {
-                                    friendView.setComment(latest.getText());
-                                    Log.d("ActivityUpdate", friendId + " のコメントを更新: " + latest.getText());
-                                }
-                            });
-                            // Observer登録済みとしてマーク
-                            observedFriendIds.add(friendId);
+                            // Observerの登録はonCreate()のfriendUserIdsLiveDataのObserverで一括管理
 
                             List<String> sortedFriendUserIds = activityViewModel.getSortedFriendUserIds();
                             int size = sortedFriendUserIds.size();