What Kernel Hearts is
Kernel Hearts is a co-op roguelike action RPG from Ephemera Games. You play as part of the M.A.H.O.U Unit, a group of four magical girls climbing the Tower of Babel to clear out angelic creatures, dethrone God, and save a world drowning in ashes. Runs are built around mixing attacks, spells, movement abilities and unique powers you pick up along the way, so each attempt plays differently from the last. Every level ends with a boss fight against that domain's guardian, so expect a real fight at the end of each stretch rather than just more trash mobs.
Playing it with friends
Online co-op lets you team up with up to four players and punch biblical monsters together. Since the run structure is shared, everyone pushes through the same tower and the same bosses, so you can split attention, cover each other's weaknesses, and stack the powers you find into combos that hit much harder than any single build. Coordination matters most at the guardian fights, where the whole group has to hold together through an intense encounter.
Between runs
After each expedition you return to a memory backup in a laboratory on the outskirts of humanity's last holdout. Run rewards go into your Unit MAHOU.OS, where you unlock and equip up to 256KB of chips and arrange them however you like. This is where your build takes shape between attempts, so a failed run still leaves you stronger for the next one. The tower also has inhabitants you can talk to and give gifts to, deepening your bonds with them as you climb.
Before you start
The tower dispels the Heavenly Curse from you, which lets you transform into your true magical girl form for a short window and unleash a devastating attack on nearby foes. That transformation is temporary, so timing it against crowds or bosses is part of the skill. Expect a difficult run: this is a roguelike, so you will die, learn the tower's patterns, and come back with better chips and a sharper plan.