Mitsurugi Kamui Hikae

Mitsurugi Kamui Hikae is a Hack and Slash doujin game made by Comic Market 84. The story of the game goes like this: Mika used to be friends with a girl name Suzuka, until Suzaka stole a demonic sword, which corrupted her, and Mika wants to stop her before the sword turns Suzuka into a literal Complete Monster, but along the way has to fight all sorts of demonic entities spawned by the sword to get in her way.

Basically, the story is an Excuse Plot for a lot of Devil May Cry style action with a bit of Soul Calibur for story flavor.

For a doujinshi game, it's short but has fairly high quality, given it's in 3D, and can be played in English via Steam.

Tropes used in Mitsurugi Kamui Hikae include:

Excuse Plot: Summarized above, and aside from some very brief cutscenes, 99% of the game is killing everything in your path.
Katanas Are Just Better: The game.
Panty Shot: Expect to see so many of these it's no wonder most fans call this Pantsu May Cry.
Turns Red: Subverted most of the time, as when enemies turn red, they are "bleeding", which means their guard is broken and they are easier to kill.
- Played straight once: after beating Sakura a second time, she glows red as the demon sword completely consumes her and transforms her into crystalline flying version of herself, which is much tougher to kill.
X Meets Y: Devil May Cry meets Soul Calibur.
Zerg Rush: Standard tactics for most enemies, but they do get somewhat more complex as the levels go by.