1813. What character can be added to both of these characters to give other characters? 加_ -> _有

Answer:

加  KA, kuwa(eru), kuwa(waru) - add, append, join, take part

有  YUU, U, a(ru) - be, exist, have

Add 貝:加+貝

貝  KAI - shellfish

賀  GA - congratulations, felicitations

賄  WAI, makana(u) - provide board, supply, furnish