Because Ainu is closed-source (despite community calls for open-sourcing), security researchers have flagged multiple concerns:

This article is for educational purposes only. The author does not condone violating osu!'s Terms of Service. Always use the official client from osu.ppy.sh .

Kinue72/hqOsu-neko: osu! relax bot/timewarp and ... - GitHub

Many players seek out custom clients like Ainu for their perceived performance benefits.

The standard osu! client renders the song selection screen, storyboards, and UI elements using CPU-bound GDI+ or, more recently, OpenGL. The Ainu Client bypasses many of these libraries. It offers: