loopy but awesome :P 
Now I'm going to let you decide who this guy is and what he wants. I have a few ideas so I'll put them down here. 
1) He's just a servant for the visiting family and was told to fetch the Prince.
2) Cooks servant bringing dinner for the Meister.
3) A thug that had masqueraded as a guest, your choice why he's there (family threatened if he didn't kidnap the prince, pauper that wants revenge etc). There would ideally be two outcomes a) Rei fights him but doesn't take in the environment, while deflecting an attack/blade it would have hit the meister and Alessandro gets in the way. It sets up some nice emotional crap there between npcs and pcs. It won't be bad because ultimately the guy isn't a skilled fighter but it'll be enough to make him need a little opium, maybe causing him to be delirious and follow into your idea. b) Because Alessandro got in front the guy grabs for him and Rei bugs out obviously. While Rei's kicking his arse he fails to see (immediately) this thugs mate who has been silent and still and quiet goes to shoot/stab Rei and Alessandro takes the second guy down receiving a glancing wound giving some nice emotional rp and see above. 

Don't have to use those ideas of course in any arrangement just thought it might be nice touch to start working on their relationship. 
Alessandro shows Rei he cares more for others than himself (getting hurt for Rei/the Meister) and inadvertently teaching him a bit about love.
Rei gets to see he is not completely unstoppable and starts seeing Alessandro as more of an equal than just his work buddy.
When Alessandro's high on Opium/asleep he could drag Rei into his bed with him and even if nothing much happens aside hugging it'll be the first step towards Rei figuring stuff out especially if he questions Alessandro and brings up love. 
Gives Alessandro a bit more dimension for me to play with. XD