Here is the full list of all 27 Kowloon High-School Chronicle achievements.
Defeated a boss for the first time.
Attacked the enemy's weakness for the first time.
Obtained your first relic
Retreat from the first battle in the tutorial without defeating the enemies.
Cleared your first quest.
Have "Dangerous human" displayed on the Report card.
Obtained purikura stickers from 11 people.
Obtained a Mini Rock Drill.
Obtained an Old Mop.
Obtained an Orange Scone from Ms. Himekawa, without her becoming your buddy.
Obtained a Garter Belt from the Black-Haired Widow.
Shoot with the Golden Gun for the first time.
Walked 10000 blocks.
Obtained all relics
Entered the extra dungeon.
Obtained the Food Soul Cleaver, Nigimitama-no-Tsurugi and Aramitama-no-Tsurugi.
Obtained SS in all grades
Have "Huanglong High School Chronicle" appear on the title screen.
Obtained all collectibles and confirmed them.
Maximized reputation with all clients.
Achieved 1st place in the Hunter Ranking.
Cleared Rockford
Obtained all room decorations.
Obtained all ringtones.
Registered all buddies and maximized their skill levels.
Defeated Izanami and Iware on the hard difficulty.
Obtained all achievements