Leveling up via killing stronger opponents

But I didn't stop. I Lunged forward, bladed fingers sinking deep into the tube I'd felt earlier before ripping into it with Jaws, Power Attacks, Crushes, and Rips. Between each attack, I Lunged back into the Nevermore's throat, tearing at the other side, before throwing myself back like a saw, shredding everything in my path with the dwindling remains of my power. Even as my lungs and limbs began to burn, I didn't let up. I didn't stop as the thrashing slowed. I didn't stop when what seemed like my entire world shook as the Grimm finally fell. I didn't let up until—

Your level has increased by one! Your level has increased by one! Your level has increased by one! Your level has increased by one! Your level has increased by one!

The windows shone brightly without actually illuminating anything—probably because only I could see them. As the messages appeared, I had to smile, despite my exhaustion and how disgusting all the various things that must have been covering me made me feel.

Then I started as I heard a disturbingly pleasant jingle and felt a thrum through the whole of my body, followed by the appearance of another window.

You have defeated the boss monster Giant Nevermore! You've obtained the title 'Grimm Slayer'!