I would have just taken it back without telling anyone.. It sounds weird but that way he can't come and ask you "did you take my fish?" because he knows in the first place that he stole it from you. Everything just hushes over that way in my opinion.. But you would have to be careful getting it back.. I realise it sounds wrong because you're basically stealing it back but then it was yours in the first place.. Its good as long as you don't get caught. (I'm not saying you should do this, this is what I would have done..) I have an Asian family too so I know keeping things under wraps creates less trouble than accusing and pointing fingers, relatives tend to blow up at nothing lol! I really hope you get your betta back one way or another..
"You are forever responsible for what you have tamed."
Betta love: it's an international thing.
Azure, Sterling, you will be with me forever. Peaches, my crazy girl, I'll miss you the most.
The Boys: Tranny, Inky "Yume" Zuko, Mao, Onishiki, Chopin, Maelstrom, Kabuki
The Girls: Kamikaze, Beeuty Qveen, Beefcake!, Chunkers, Awesome Sauce
Meeces: Koko, Bijli, Baadal, Barkha
Turtle: Hi Handsome (female -__-)