In addition to Bullet Heart, this game's a really tight realtime puzzle game that prioritizes a balance of quick thinking, character mastery, and risk-taking to succeed. There's a lot to love for players who are fans of Touhou and similar bullet hell titles, as it draws direct inspiration from those games and their PVP-style entries.
For players unfamiliar to Bullet, it's a game of absolute survival trying to clear incoming bullets from your opponents or the center bag as efficiently as possible while managing a small pool of AP and patterns with positional requirements as a resources. It's an elegant and fast-paced little game with lots of playstyles to choose from in the form of its characters.
There's also an excellent raid-style solo/co-op Boss Battle mode that feels pretty inspired by games like Tetris Effect: Connected.
An absolute recommend for people looking into this niche style of game.