Okay, a couple of thoughts...
1. Vertical/portrait mode. Not b/c all portraits have to be shot in portrait mode. But b/c there is nothing in any of these shots that screams out for a landscape mode. Now...if one of the them had been horizontal...or it had been a group of people...or there was a prop (like a vehicle)...then horizontal is the way to go.
2. So many cosplay portraits miss such rich possibilities. They're shot at cosplay conventions so you get a hotel lobby with a bunch of people milling around. If you could find some space (a blank wall) and add a few props (print out a poster ahead of time or something else that is cheap to make or suggest) to add to the portrait. For instance, if you're shooting a Red Sonja, get 1 or 2 costumed characters to lay in the background like dead bodies (and then blur them). If you're shooting a Japanese manga/anime schoolgirl than add a couple of books stacked like she's hauled them from school. And eliminate a lot of that background clutter (yeah, I know, DoF blurs it). But 98% of the cosplay portraits I've seen have screamed "I'm at a convention--can't you tell?" Maybe the hotel has a garden. Or there is a hint of newer or older architecture that fits with the character somewhere around the hotel. Or you can get a prop from a restaurant (like a pair of wooden chopsticks for an anime character). For example, I once saw someone do a Cosplay of Vesper Lynd (the Bond Girl from Casino Royale) and they got a martini from the hotel bar and posed her with that.