I don't know how or particularly when this became a thing but Sephiroth feels a responsibility for Ib that he just doesn't have over others. I'm starting to think this is partly due to her 'giving it her all' attitude that he had when he was her age, along with perhaps a minor projection of the things he lacked in his own childhood.

Depending on how the fallout goes after the last event, and if he hears the suggestion/Spencer might suggest it, he may or may not offer to take her for a day out in TG closer towards the end of the month - as something of a parting gift since he'll be moving to Esdham for a while soon.