While I feel like Satoru is the likelier fit for being Suyin's dad, the theory that it's Sun has a special place in my heart purely due to how wonderfully it would fit in with weilin.
His background is quite similar to Bolin's and his relationship to Toph is really cute from what I've skimmed. But the idea of Wei's grandfather being a lavabender and him also falling for a lavabender does tickle my fancy.
It would also be fun with how many direct paralels I notice between how Toph was raised and how her grandchildren were.














