What Mitsume is
Mitsume is a two-player cooperative horror game set on a dimly lit university campus. You and one partner walk through the same map, but each of you sees something the other does not: exactly one object or detail differs between your two views. That difference is the "Anomaly." You explore in first person, open doors, and keep an eye out for anything that looks wrong on your screen while your partner checks their own.
The loop is simple. Find the anomaly, describe it to each other, then both players stare at it together for a set amount of time. It gets resolved, and you are sent back to your starting position to hunt for the next one. The goal is to clear as many anomalies as you can by repeating that cycle.
How the two of you play together
This game is strictly two players on two devices. There is no solo mode and no AI partner, so you need a real person alongside you. Since the game has no built-in voice chat, you have to talk through something else — a call, a voice channel, sitting in the same room. Without communication the game does not work, because neither of you can see what the other sees.
Talking is the actual mechanic. One of you notices something odd, describes where it is and what it looks like, and the other confirms it from their side. Progress comes from comparing notes and from both of you looking at the same spot at the same time.
What to know before starting
There is a time limit on each anomaly. Miss it and an unstoppable monster appears, which ends the run. A mysterious third figure also wanders the map and can transform into the three-eyed monster Mitsume to attack you. You can drive it off by staring at it together, but getting caught twice ends the game.
Controls are keyboard and mouse: WASD to move, mouse to look, hold right-click to stare, left-click to open and close doors, Esc for the menu. A playthrough runs about 20 to 40 minutes. The supported language is Japanese, so keep that in mind before you start.