VIVIT-99R
2VIVIT-99R is the latest April's Fools joke from the developer of Seihou, the on/off sister project to Touhou. Incidentally, it also was last year's April's Fools joke, only back then, it was called VIVIT-99 and only pretended to be a Battle Royale multiplayer game, and you were actually just fighting bots. Not so this time! VIVIT-99 has [R]eturned with actual multiplayer, actual leaderboards and actual possibility to start a new game and immediately get blasted by a player with a much higher level than you.
Here's the rules:
Graze bullets to raise your level (bottom-left corner) and attack other players. The higher your graze counter (top-right corner), the more level you will gain when an enemy wave is over. The higher your level, the stronger your attacks against other players. Your attacks will prioritize the player with the highest survival time (top center), which in turn means if you survive for a long time, everyone else will start vomiting bullets into your game. Getting hit reduces your HP (top-left corner) and gives you a VERY brief invincibility period - you can lose all HP from a single line of bullets if you don't move out of the way immediately. If HP drops to zero, you lose. There is no way to regenerate HP.
And here's the game!
https://v99.ss-do.com/