Here is the full list of all 15 Gunvein achievements.
Complete both tutorials.
Get your first score-based extra life.
Finish the game on Mild difficulty or higher.
Finish the game on Intense difficulty or higher.
Finish the game on Expert difficulty.
Complete all the special requirements on any Score Rush Mission.
Complete Boss Rush on Intense difficulty or higher.
Clear Arcade Mode.
Clear Arcade Mode on Intense or higher.
Clear Roguelike Arrange.
Clear Roguelike Arrange with a starting difficulty of 10 or more.
Unlock 9+ continues.
Bomb right as you're about to die & save yourself.
Reach a score of 3,000,000 in Arcade Mode.
Get a 1CC while using 5 or less bombs/hypers.