It's made by the original artist/author so it kind of is the original manga.... yeah.. I hate myself too. Artsy_nela
It is NOT made by the author... But by the group Nanana Nana... Someone need to change that ! Moreover you can SEE the art style is completely different. Also it's not a side story to the manga but a doujinshi
I thought this was the original manga.... y would you do this?