Here is the full list of all 11 Under One Wing achievements.
Clear Nahoko's Route
Helped settle the score with an old rival.
Clear Mimari's Route
Made things crystal clear to your "rival."
Clear Kazusa's Route
Saw the end of a sibling rivalry.
Clear Hikari's Route
Gave it everything you had, but in the end...
Saw the fight postponed for another day.
Clear the Common Route
Welcome to Under One Wing!