What character is this man with a gigantic, red-white-black, mace-like weapon cosplaying as in Hyper Japan?
Asking around on Discord, that character is actually not from an anime or manga but rather from a game titled League of Legends. It's a skin from one of it's characters named Jayce. Not sure if this would be considered on topic, then. I'll leave it up to those who know better.

Anyway, here's a picture for comparison:


Credits goes entirely to Discord user 'Untarnished' who identified it.