Translation:Will you cosplay with me?
"Why don't you cosplay with me." can be a statement or request but is softened because it's being asked as a question. I don't think he means the other person expressed unwillingness. I use this form all the time "why don't you do ___" to make a soft request. I guess this is too subtle though maybe.
Haha, maybe one of the most weak category in the Japanese. As the Japanese is not so emotional apparently.
Please try like this: http://www.imdb.com/list/ls051850302/
There are a lot of traditional romance, but those in the list are mostly for the younger generation. I can recommend 'hidamari no kanojyo' in the list.