These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Flat Character: Ion Green, yeah, she may be a more than 200 years old teenager which is the key to inmortality and being the antidote for the N5S Virus but she barely has anything to do with what was happening, and the fact that the manga has some Mind Screw here and there it's kinda easy to lost track of her, and hard to see her as a character rather than a Plot Device.