I feel like people need to keep in mind that from KG Shion's perspective, Takumi

>shows up
>says he's from the future
>kills a guy who hadn't done anything
>then kills Gaku (because of G'ie infection that is later removed by timeline-hoppers)
>Then says "Hey everyone, let's join this Killing Game", which proceeds to get more people killed indirectly

Like, I feel his skepticism is more than justified and he actually gives Takumi way more benefit of the doubt than most people would if this was their first introduction to someone. Lay off.