Creative idea! I really liked how you used different kinds of syllables to add to the character of each enemy (I really liked the second guy who says stuff like nyanyanya and hahaha!)
Agreed with bulbandrei that it's a little confusing at first - I didn't realise I had to type a number before I could type one of the attacks. Also, I think some more feedback on the amount of damage your attack does could be good - I assumed while playing that longer words do more damage, but I was never actually sure.
One other thing is the 4th enemy's sound effects are super loud ahaha - maybe turn him down a bit!
I can imagine you turning this into a fun Japanese Kanji learning game, where you have to beat enemies by typing the right readings for different characters or something!