Here is the full list of all 25 Baldr Sky achievements.
Complete Makoto Route Ending 'Makoto'
Complete Makoto Route Ending 'Object Loss'
Complete Rain Route Ending 'Ghost'
Complete all reminiscence events.
Complete stage 50 on (Dive 1) survival mode.
Complete Aki Route Ending 'Ark'
Complete Aki Route Ending 'Nirvana'
Complete Aki Route Ending 'Aki'
Complete stage 25 on (Dive 1) survival mode.
Complete Chinatsu Route Ending 'Departure'
Complete Chinatsu Route Ending 'Chinatsu'
Complete Chinatsu Route Ending 'Entwined'
Complete Nanoha Route Ending 'Nanoha'
Complete Nanoha Route Ending 'Embrace'
Complete Rain Route Ending 'Rain'
Complete Chapter 1
Complete Nanoha Route Ending 'Dream Land'
Complete Final Route Ending 'Sora'
Complete stage 75 on (Dive 1) survival mode.
Complete stage 100 on (Dive 1) survival mode.
Complete stage 25 on (Dive 2) survival mode.
Complete stage 50 on (Dive 2) survival mode.
Complete stage 75 on (Dive 2) survival mode.
Complete stage 100 on (Dive 2) survival mode.
Complete the true ending.