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