Anyone knows the title of the manga?
The main characters are 2 young siblings (male and female) who are actually acting as agents for monsters / aliens whom are destroying world / humanity. They changed cities / location after the monsters / aliens destroyed the previous cities they lived in. I only read the first chapter or two at least 5 years ago iirc. (it only had 1-3 chapters released, again iirc).

Despair trigger?

Ah, seems like that's the one. Oh it was only a one-shot and only ~2 years ago, huh. Lol. 😀
Thanks a lot for identifying that!