Flash of the Blade X

Flash of the Blade X is a first-person slasher set in Feudal Japan.
Take control of a ninja on a quest for revenge against the clan that betrayed him and left him for dead.
Use period-accurate weaponry such as the Katana, Kusari-Gama, and Shuriken to bring death upon enemies.

Résumé

Flash of the Blade is a first-person slasher with a high level of difficulty due to its one-hit-kill mechanic. Described by testers as unforgiving, brutal, and thematically on-point, the game has gone through extensive balancing to get it to a stage where it is no longer unfair, but FUNfair.

The game is purposefully light on story, basing itself around a battle between a lone ninja and an Evil Ninja Clan helmed by a diaper-wearing Sumo. Expect to suffer not just due to the game's difficulty, but due to seeing the boss in a giant diaper.
The story effectively boils down to - See Ninja, Fight Ninja, Be Ninja.

Flash of the Blade contains 11 fast-paced, ferocious levels, 5 deadly weapons, and 6 grueling enemy types.