Unlike the official osu!lazer (the future of osu!) or the classic Stable (Fallback) client, the Ainu client removes nearly all visual and background processes deemed "unnecessary" for raw gameplay. Think of it as the difference between driving a luxury SUV versus a stripped-down Formula 1 car. The Ainu client prioritizes frames per second (FPS) and input latency above all else.
While the Ainu server itself is a long-standing project, the official osu! stance is generally to be cautious. Using third-party clients or private servers can involve sharing account credentials with third parties, which may put your main account at risk. Additionally, playing on private servers won't get you banned from the official game, but using cheats or certain modifications can lead to a ban if you try to switch back to Bancho with them active. How to Get Started osu ainu client