That was nice, I think their relationship works really well for an adventurer group. They can still marry each other when they settle down one day. It needs more kinky yuri demons, catgirls and futa in the future though.
SSR is the highest rarity for gacha characters you have to get through luck (or lots of money). The chances to get one of these is often around 1%. So SSR in this context just means he's super special and great.