Most likely, you are either referring to a specific skin/theme, or this is a typo for another popular client.
Kinue72/hqOsu-neko: osu! relax bot/timewarp and ... - GitHub osu ainu client
Unlike modern "blatant" cheats that spin your cursor at 1000rpm, the Ainu Client focused on undetectability. Key features included: Most likely, you are either referring to a
"osu!" is a free-to-play rhythm game primarily developed by Dean "peppy" Herbert in 2007. The game allows players to play along with music to various levels of difficulty, with a strong focus on community-created content. Players can download and play a vast array of user-created beatmaps, which are essentially custom levels made by the community for almost any song imaginable. The game supports various play styles, including Osu!standard (which involves clicking on circles, sliding on sliders, and spinning spinners), Taiko, CtB (Catch the Beat), and Mania. - GitHub 2
client designed to connect to the Ainu private server. It is often used by players seeking a different community experience, custom ranking systems, or features like free osu! Direct. Key Features of the Ainu Client
Incognito Mode: Hides a player's identity and activity from Discord Rich Presence and live streams.
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