nash is an only child as well, so he'd love a pseudo sibling to break apart the stuffiness of adults that he grew up around. he pretty much spent his hogwarts years intimidated by letting people in too closely, so having at least one that he allowed himself to connect with would be good for him. that's pretty badass, little torrin already having a hand in wandless magic when he was just figuring out magic. it could be a situation where they met when he was having a little out of control magical episode and their bond started from trying to zen one another out? they kept in contact and it spidered out into a sibling bond? or they could have ran into each other in a calmer setting and they were just casual friends for a bit until torrin had some uncontrollable episodes and let nash in on them and he tried to help talk him through them, thus deepening that friendship relationship into a more sibling feel?