Here is the full list of all 35 RKGK / Rakugaki achievements.
Finished the first level
Defeated Mr. Buff
Defeated Sunflower Noodle
Defeated Tentacle Tangle
Defeated Machine Onslaught
Defeated War-O
Purchased your first Gear
Purchased your first Graffiti design
Purchased your first Paint Job for AYO
Completed your first Timer Challenge
Activated Defacer Mode at least once in every Level
Completed all EXE Levels
Defeated Mega Buff
Completed all Timer Challenges
Purchased all Gear
Purchased all Paint Jobs for AYO
Purchased all Graffiti designs
Collected all in-Level Ghosts
Destroyed every box in every Level
Painted all Graffiti Propaganda and Billboard spots at least once
Defeat any Boss without taking any damage
Completed the Level “Gray Inferno” without triggering a spotlight
Concluded Valah's journey... for now
100% all Levels in Chapter 1
100% all Levels in Chapter 2
100% all Levels in Chapter 3
100% all Levels in Chapter 4
100% all Levels in Chapter 5
100% all Levels in Chapter 6
Defeated all Bosses without taking any damage
Completed EVADE.EXE in less than 1 minute
Completed "Machine Onslaught" without using Glide/Grappling Hook to destroy an enemy
Completed the game in less than 1 hour 40 minutes
Amassed 200,000 Coins
Complete all achievements