After posting a teaser picture on Dec 2nd, Rayark released a preview video of a collaboration between Cytus II and Arknights. It introduces the main character Amiya and a few playable songs such as Boiling Blood and ManIFesto.
According to precedent, players can generally obtain the crossover content pack for $9.99, usually including around 10 tracks. There will also be character stories from Arknights that players can unlock by playing songs.
This crossover event is on Cytus II only; Arknights will not be holding a collaborative event.
Cytus II is a rhythm game by Rayark. Players can tap the notes following the music, and it also contains several characters and stories that took place before the events of the first game. Arknights, on the other hand, is a tower defense game with gacha mechanics.