Last weekend I went to an event to take some cosplay pictures and I published them in my twitter account, previous cosplayers' authorization. Today, I got a DM from one of them, which seems to be a professional cosplayer working under a company (not the event's host), since the message was addressed from a company person. He is asking me for one of the pictures to use on a calendar.
This is where I'm getting confused, since they want to use a picture taken from me for one of their employees. Am I the legal owner of the pictures? If so, should I proceed to charge them for the photo?
If there is of any help, the event was the Comiket 97 at Tokyo