Red Ronin

You can check the walkthrough section to see how to easily complete the game without dying and under 1 hour.

Here's the link:
https://www.trueachievements.com/walkthroughfull.aspx?walkth...

The achievement might be buggy in a good way: I just finished the game in 3:35:18.19 and still unlocked it BUT I didn't unlock the basic achievement for finishing the game, they might be switched around or have the wrong description.
To realistically beat the game in less than 1 hour you'll have to learn every single stage and room perfectly and die very few times, I lost a lot of times replaying some rooms that looked impossible at first, also the last 2 bosses can kick your ass and make you lose a lot of time. The developer said on Steam that "after beating the game you can access every stage via computer (MU Stages) or death list (Normal Stages). The stage's stats (deaths, rank, etc...) are replaced if you make a better score than the previously recorded one." but that wasn't the case for me, after beating the game and seeing the credits I could only continue from the last cutscene and watch the credits again or start a brand new game deleting my previous save. I might try a sub 1 hour run after learning every room perfectly and upload it in the future!