While the demographic is probably because of where it's published in or something, this is most definitely not seinen. It sure looks like it's trying hard, with an angsty ossan as a MC, but he's literally acting as a guardian for a loli (+more later) who uses plungers for arrows because she doesn't want to hurt monsters. Then she literally defeats the first boss using the power of friendship and her plunger arrow.

Side note: said boss is a spirit of a forest that's pissed that humans have been deforesting then land and then literally enslaving the demi-human population. She screams that the forest lord should 'love us again'.

....

There are so many things wrong with this series that i just cringe. Frankly I was hoping that it'd end up like nice fluffy slice of life or something - I could see that and it might go over well. Nope, the series TRIES to be serious, and takes itself seriously without an ounce of self-mockery or parody, and ends up as an utter joke. It just ... doesn't work.