Games like Gen'ei ninja
Games like Gen'ei ninja include NINJA GAIDEN: Ragebound, SANABI, The Messenger, Katana ZERO, and Super Meat Boy. We matched them by the tags players give Gen'ei ninja on Steam (2D Platformer, Action, Ninja, Side Scroller, and Pixel Graphics): closest matches first, and among equally close ones the better-known games.

NINJA GAIDEN: Ragebound
Shared: Action · Ninja · 2D Platformer

SANABI
Shared: Action · 2D Platformer · Pixel Graphics

The Messenger
Shared: Retro · Ninja · Pixel Graphics

Katana ZERO
Shared: Action · Pixel Graphics · 2D Platformer

Super Meat Boy
Shared: 2D Platformer · Pixel Graphics · Indie

Broforce
Shared: Action · Pixel Graphics · Side Scroller

Shovel Knight: Treasure Trove
Shared: Pixel Graphics · Retro · Action

Gravity Circuit
Shared: Action · 2D Platformer · Pixel Graphics

SHINOBI: Art of Vengeance
Shared: 2D Platformer · Action · Ninja

Pizza Tower
Shared: 2D Platformer · Indie · Pixel Graphics

Skul: The Hero Slayer
Shared: Action · Indie · Pixel Graphics

Celeste
Shared: Pixel Graphics · 2D Platformer · Indie

Terminator 2D: NO FATE
Shared: 2D Platformer · Side Scroller · Action

Bloodstained: Curse of the Moon
Shared: Action · Pixel Graphics · Retro

Mark of the Ninja
Shared: Ninja · Action · Indie

Cyber Shadow
Shared: Ninja · Pixel Graphics · Retro

Teenage Mutant Ninja Turtles: Shredder's Revenge
Shared: Side Scroller · Pixel Graphics · Ninja

Downwell
Shared: Pixel Graphics · 2D Platformer · Action

UFO 50
Shared: Action · Pixel Graphics · Indie

VVVVVV
Shared: 2D Platformer · Pixel Graphics · Indie

Sonic Origins
Shared: 2D Platformer · Action · Pixel Graphics

Mark of the Ninja: Remastered
Shared: Ninja · Action · Side Scroller

Huntdown
Shared: Action · Side Scroller · Pixel Graphics

Rogue Legacy
Shared: Action · Indie · Platformer