 If you liked
Monster
|
 ...then you might like
Kiseijuu
|
Both manga explore the same question - What separates human from monster?
Monster does this via a character drama exploring the monster within all of us, as its protagonist chases what he see as the biggest monster of all.
While Kiseijuu does this via showing the contrasting differences and hypocritical opinions between humans and the alien parasite, as its central pair continue to grow closer together from a mental state of position.