That's a weapon based off of Battle of the Immortals, is it?

No, it's a Great Sword from Monster Hunter (A Ravager?). And further ahead is a Lance user, though I can't tell what kind.

Exactly how is this Shadow of the Colossus?

suzukijirotto said:
Exactly how is this Shadow of the Colossus?

Maybe it's a parody of one of the Shadow of the Colossus art? I know I've seen this somewhere before, and the tags on Pixiv also refers this to that of Shadow of the Colossus.

The tag in question was added by a user, not the artist; also, what it actually says is むしろワンダと巨像, "more like Shadow of the Colossus", so tag removed.