Smut-
Remus has a tentacle dick along with his normal tentacles out his back. (Side) decides to gift Remus their first time for his birthday but becomes quite surprised when he sees his tentacle dick but is more than willing to still do it with him.

Birthday idea-
Everyone surprises Remus with a free pass to do whatever he wants for his birthday, unless it was something that could seriously hurt one of them or it's something that a side has put on a 100% off limits list. He just lets his impulses go haywire for the day but not doing anything to make a side hurt or uncomfortable with their off limits list, causing havoc all day but it's nice to see Remus happy the others thought.

Angst-
(This idea had the thought of Logan in mind but it can be any side)
Remus doesn't think that anyone remembers his birthday, nobody said happy birthday or gave him a gift. He's upset all day and is just ready to go back to sleep how upset he is. But he later finds a music box in his room when he finally gets back with a note on it. "Happy Birthday, Remus. Sorry I didn't say anything about it all day, I was very busy but I did indeed remember. A music box, for your birthday. Please enjoy it. Signed; (Side)" Remus almost cries before rushing to (Side)'s room to thank him and maybe cry on his shoulder.