Wait, wouldn't Kichikujima be the sequel? Since Marie looks like she's a child in this one, and is a teenager in Kichikujima.
(edit: looks like it's been fixed now )
*Read in David Attenborough's soothing voice*
Many mangakas are afflicted with a condition in which they never outgrew their chuunibyou.
The main sympton is when they mistake edginess for drama. This has unfortunate consequences.
Here, we can see some of the disastrous results.
The thing with this manga is that it is kinda goofy and does not take itself seriously. A much better read would be The World is Mine. Although it also has elements of supernatural it's not goofy - it depicts peoples reaction to serial killing and hostage situations in somewhat realistic fashion.