Shinsekai Into the Depths is an underwater side-view exploration game where you play a survivor in an old diving suit, slowly going deeper and deeper as the world above freezes over.

The basic gameplay is explore the environment, find resources (by killing sea creatures or mining with your pickaxe), craft weapons and upgrades, and upgrade your suit so you can explore the next underwater layer.

Hit points is pretty much your air supply. You have an internal tank and can pick up five external tanks (and another five with an upgrade). When you take damage it comes off of your external tanks first so they get damaged and eventually are destroyed, reducing your air capacity. Air is also used to jet propel yourself around (reducing fall damage or going up a shaft). Luckily lots of air streams can be found emitting from the ground and every save point has an air stream.

It's a fairly chill game with few dangerous monsters. Mostly exploration and trying not to damage your suit much while keeping your air supply high. You have to hit levers to open doors and you find artifacts to examine including hand drawings trying to explain things to you (like what's coming up ahead or telling the plot). There is no dialogue other than help text, nor voice overs, and no real action music. Watery sounds and you moving around.

Nice graphics. I was playing with a controller and it's not extremely responsive though I suppose that matches being in an ill-fitting diving suit. But after an hour this game is a bit too chill for me so time to move on to another game.