Slime Story (2010)

From Introduction:

I had the idea for the Slime Story setting while I was playing a free Korean MMORPG. My character was a girl with red pigtails, and thanks to paying for some customization, she was running around in a pleated skirt, raglan T-shirt, red tennis shoes, and headphones, swinging a big spiked pole arm thing at cute monsters. I wondered what kind of world she might live in, and Slime Story was born.

One-way magical portals provide a constant stream of cute monsters, and many teenagers go out and hunt those monsters. They collect parts from the monsters, and trade those in at the Monster Mart at the mall. They get exercise, spending money, and time with friends. Of course, that doesn’t stop them from acting like teenagers. They make friends and sometimes enemies, they fall in or out of love, they piss off their parents, and so on.
There are other things going on in the world—there are distant countries where men are fighting bloody wars over control of portals—but here and now, there are teenagers living their lives and hunting monsters to stay sane in a little town where nothing ever really happens.