It happened the same to me, I couldn't find any way to attack. I had to set up my keyboard layout shortcuts to be able to switch to the Japanese one. The key attack is the one next to right shift. Shift itself is for blocking so... it makes sense I guess.
The game looks cute but it feels too easy (at least up to the first boss) and the lack of any combo won't help making the combat entertaining. Simply try to sneak behind an enemy and backstab damage, wait till they get close and attack during their attack animation. Oh and jump attack says "Effective" and deals extra damage. But that's it.
It actually reminds me of another similar game, with also chibi characters going through dungeon floors but using magic, I forgot its name.
And it's [loli] indeed.