MC is sent back in time to murder the monster slayer before she becomes too powerful to kill. Starts off feeling like a slice-of-life shoujo, but it ramps up into a more shounen like fighting manga. Reminds me of My Hero Academia, in that there's a lot of cliche's (like the hero association, girl falling in love with the guy without him noticing, etc), but it's still done well enough and with a few plot twists that it's interesting.
Her Hero