If you have played or have heard of a game called Domekeeper on steam then you will be right at home with this game. To describe it simply, this game is Domekeeper mixed with Vampire Survivors.
Like Domekeeper, your main method of acquiring upgrades and currency is by mining underground for them. Unlike Domekeeper where you have a Dome and you dig directly below it, here you have a deep-sea diving mech that can maneuver around to the various caves to mine for resources but the core loop is the same: find and mine resources, bring said resources back before the next wave of enemies approach.