Zuno, also called (Brain Cell Revival Game) is a minigame within Forbidden Siren. To unlock it pick up the Brain Cell Revival Game (Archive Item 87) during Kyoya Suda's Mission (Day 3 - 03:00) in the nest.
Line up like colors to make them disappear and get points. You can hit a button to add more random units to the board, but they also appear over time.