Games like Demonizer
Games like Demonizer include Bit Blaster XL, BALL x PIT, Bot Vice, Chippy, and Sky Force Reloaded. We matched them by the tags players give Demonizer on Steam (Shoot 'Em Up, Top-Down Shooter, Bullet Hell, Difficult, and Shooter): closest matches first, and among equally close ones the better-known games.
Bit Blaster XL
Shared: Shoot 'Em Up · Bullet Hell · Difficult
BALL x PIT
Shared: Bullet Hell · Shoot 'Em Up · Arcade
Bot Vice
Shared: Top-Down Shooter · Shoot 'Em Up · Bullet Hell
Chippy
Shared: Bullet Hell · Shoot 'Em Up · Top-Down Shooter
Sky Force Reloaded
Shared: Shoot 'Em Up · Bullet Hell · Top-Down Shooter
Planes, Bullets and Vodka
Shared: Shoot 'Em Up · Bullet Hell · Arcade
Touhou Koumakyou: New Classic - the Embodiment of Scarlet Devil
Shared: Shoot 'Em Up · Bullet Hell · Difficult
LUFTRAUSERS
Shared: Bullet Hell · Shoot 'Em Up · Arcade
BLUE REVOLVER
Shared: Shoot 'Em Up · Bullet Hell · Arcade
ZeroRanger
Shared: Shoot 'Em Up · Bullet Hell · Arcade
Touhou Tenkuushou ~ Hidden Star in Four Seasons.
Shared: Bullet Hell · Shoot 'Em Up · Difficult
Nova Drift
Shared: Shoot 'Em Up · Bullet Hell · Arcade
Nuclear Throne
Shared: Difficult · Bullet Hell · Top-Down Shooter
Enter the Gungeon
Shared: Bullet Hell · Difficult · Pixel Graphics
DoDonPachi Resurrection
Shared: Shoot 'Em Up · Top-Down Shooter · Bullet Hell
Touhou Kinjoukyou ～ Fossilized Wonders.
Shared: Shoot 'Em Up · Bullet Hell · Shooter
Phoenix Force
Shared: Bullet Hell · Difficult · Top-Down Shooter
Assault Android Cactus+
Shared: Shoot 'Em Up · Bullet Hell · Difficult
Mushihimesama
Shared: Shoot 'Em Up · Bullet Hell · Arcade
Ikaruga
Shared: Shoot 'Em Up · Bullet Hell · Arcade
Touhou Juuouen 〜 Unfinished Dream of All Living Ghost.
Shared: Shoot 'Em Up · Bullet Hell · Shooter
Super Star Path
Shared: Shoot 'Em Up · Top-Down Shooter · Bullet Hell
Vampire Survivors
Shared: Bullet Hell · 2D · Pixel Graphics
Star of Providence
Shared: Bullet Hell · Shoot 'Em Up · Difficult