Also known as: ネコアルク
Alternative Chibi version of Arcueid Brunestud. Appeared first in Tsukihime during the bad ending offering advice to players to help them. Later she became a full-fledged new character in Melty Blood being playable and getting a sleeker design. Inspired the Neco Spirit race.
If the post is only referencing Tsukihime, then just tag Tsukihime. Otherwise, tag Melty Blood.