He can shapeshift his features whenever he wants
He just likes to keep his fins-

Lou will always love you
Unless you kill a spider
Then he's hesitant
Or if you hurt/kill his friends
Then he hates you-

Roman can kill someone by a kiss
Basically taking away their life source while he kisses them
Like a kiss of death
But don't worry about Lou tho
He can always return the life source back-

He chose Lou as his victim because Lou killed him before and he wanted payback