Manga 127907 Kaijuu 8-gou Userrecs

Main character suddenly gets demon powers and dragged into a world of demons. The powers they get are from an insanely strong demons feared by the other characters and demons. Both set in a form of Japan with an organisation set up to get rid of those monsters. 

Both have a witty and optimistic humor, with funny and action-filled fights, captivating characters and of course... DESTROY YOUR ENEMIES WITH ONE PUNCH! 

Both Manga don't necessarily do something new, but will draw you in anyways through their highly fast paced action, intriguing storyline, extremely likeable characters and the genuine level of heart felt in every aspect of the manga. 

Captures a similar feel to early AoT before it tried to get philosophical. It definitely takes some inspiration but not similar enough to call it a knock-off by any means. It currently a very fun action title. 

Very similar feel with an organisation built around destroying villains/kaiju. Main characters both start off extremely weak and quickly get a broken power. 

Aliens Area is an alien version of Kaijuu 8-gou pretty much. It isn't play for laughs as much, but it also doesn't take itself too seriously. I have read very little of both manga, but the basis of the story is very similar I feel. I finished chapter 4 and there is 0 fan service in the manga so far, I hate fan service so I greatly appreciate its absence in this manga. 

Both World Trigger and Kaijuu nr.8 have a strong sci-fi-esque ambience, and if you're into that aesthetic, I recommend checking out either series! But that is not the only similarity! In both cases, the city is in constant danger from monsters appearing, and the protagonists are specialized in defending the city. Well, that's a strong similarity! But wait, it gets even stronger: while the standard weapons depend on the individual's abilities and creativity, there are some rare personalized weapons, that require the user's compatibility and that are made from other people's sacrifices. So, if any of those aspects captivated you in one series, you might enjoy it in the other title as well!  

Gantz and Kaiju #8 share some similarities with their general premise: -Monster tech in the form of power suits and weapons = Alien tech in the form of power suits and weapons. -Overwhelmingly powerful monsters that are large-scale threats = Overwhelmingly powerful aliens that are large-scale threats. -MC has a childhood friend who he wants to be like and stand alongside = MC has a childhood friend who he eventually wants to be like and stand alongside. -MC can't risk revealing his secret power = MC can't risk revealing his secret alien hunting sprees. 

very similar monster designs funny story with some dark elements the main character is a monster with transforming powers girls like main character  

The two are similar in that the hero is no longer human and has become either a monster or a demon. 

They both have main characters who don't want to be the best of the best - Both series contain supernatural monsters (kaiju and Phantoms) and exorcising so called monsters - Both titles can delve into some pretty dark stuff and have a similar vibe - both title have some supernatural stuff