diff --git a/mihomo/tools.py b/mihomo/tools.py
index 44e5223f..63682531 100644
--- a/mihomo/tools.py
+++ b/mihomo/tools.py
@@ -1,11 +1,20 @@
 from typing import TypeVar
 
-from .models import StarrailInfoParsed
+from .models import Character, StarrailInfoParsed
 
 T = TypeVar("T")
 
 
 def remove_empty_dict(data: T) -> T:
+    """
+    Recursively removes empty dictionaries from the given raw data.
+
+    Args:
+        - data (`T`): The input data.
+
+    Returns:
+        - `T`: The data with empty dictionaries removed.
+    """
     if isinstance(data, dict):
         for key in data.keys():
             data[key] = None if (data[key] == {}) else remove_empty_dict(data[key])
@@ -16,7 +25,56 @@ def remove_empty_dict(data: T) -> T:
 
 
 def replace_trailblazer_name(data: StarrailInfoParsed) -> StarrailInfoParsed:
+    """
+    Replaces the trailblazer name with the player's name.
+
+    Args:
+        - data (`StarrailInfoParsed`): The input StarrailInfoParsed data.
+
+    Returns:
+        - `StarrailInfoParsed`: The updated StarrailInfoParsed data.
+    """
     for i in range(len(data.characters)):
         if data.characters[i].name == r"{NICKNAME}":
             data.characters[i].name = data.player.name
     return data
+
+
+def remove_duplicate_character(data: StarrailInfoParsed) -> StarrailInfoParsed:
+    """
+    Removes duplicate characters from the given StarrailInfoParsed data.
+
+    Args:
+        - data (`StarrailInfoParsed`): The input StarrailInfoParsed data.
+
+    Returns:
+        - `StarrailInfoParsed`: The updated StarrailInfoParsed data without duplicate characters.
+    """
+    new_characters: list[Character] = []
+    characters_ids: set[str] = set()
+    for character in data.characters:
+        if character.id not in characters_ids:
+            new_characters.append(character)
+            characters_ids.add(character.id)
+    data.characters = new_characters
+    return data
+
+
+def merge_character_data(
+    new_data: StarrailInfoParsed, old_data: StarrailInfoParsed
+) -> StarrailInfoParsed:
+    """
+    Append the old data characters to the list of new data characters.
+    The player's info from the old data will be omitted/discarded.
+
+    Args:
+        - new_data (`StarrailInfoParsed`): The new data to be merged.
+        - old_data (`StarrailInfoParsed`): The old data to merge into.
+
+    Returns:
+        - `StarrailInfoParsed`: The merged new data.
+    """
+    for character in old_data.characters:
+        new_data.characters.append(character)
+    new_data = remove_duplicate_character(new_data)
+    return new_data