diff --git a/src/arcaea_offline/utils/partner.py b/src/arcaea_offline/utils/partner.py
new file mode 100644
index 0000000..3ec4a61
--- /dev/null
+++ b/src/arcaea_offline/utils/partner.py
@@ -0,0 +1,15 @@
+from datetime import datetime
+from enum import IntEnum
+
+
+class KanaeDayNight(IntEnum):
+    Day = 0
+    Night = 1
+
+
+def kanae_day_night(timestamp: int) -> KanaeDayNight:
+    """
+    :param timestamp: POSIX timestamp, which is passed to `datetime.fromtimestamp(timestamp)`.
+    """
+    dt = datetime.fromtimestamp(timestamp)
+    return KanaeDayNight.Day if 6 <= dt.hour <= 19 else KanaeDayNight.Night