After hearing her backstory Rinta gets a temporal power up and carries her through the snow storm on his own, takes her back to the Inn in time and she gets hospitalized, he passes out upon arriving, that's when her father comes to check her. He isn't worried about her as family but as an asset that still is useful and would be a waste she died whe finally found an use for her.
Eventually they find a photo of his late wife, it's just Fumi but Milf, why? Even Rinta could tell by just looking at the photo. That's wen her fahter admits it.
Fumi is actually THE biological elder daughter, his wife was expecting twins but it was a risky pregnancy which lead to her death due to massive blood loss during childbirth and because Rana was still premature during Fumi's birth she still got sent to ICU for half a year until she was stable, Fumi got put into adoption out of spite.
Then years later when he wanted to become the chairman Fumi became useful for clout and adopted her back, all that shit about being adopted and underserving of a true family was just him being petty for the death of his wife, Rana was just following his example as shitty father could raise her to be.
Rinta accused him of being a shitty manchild and he hit Rinta in anger and he bled as usual(I swear this guy would lose to an infant in a fight but he somehow fought back well to playboy back then, maybe isn't weak but has a funny blood issue) but shot back that his flimsy fists couldn't hurt him for real as he passed out, Rana heard the truth while she was hidden during this event.
Fumi is being set up as a pawn for an arranged marriage but it seems Rinta manages to ruin it by crashing it all with a letter he sent to her throught Rana.
She just leaves in the middle of the party special host talks embarrasing her father and Rana telling him to let her go becuase of them she was miserable, just look at her run, she finally found happiness.
She goes back to college and is happy, MC once again tells her how she loves her and she takes him to bed like Rinta is the princess here (lmao yes, you read it right)
Hopefully they don't get interrupted and also I hope isn't just the final arc, I've liked the story and has been far better than the Guilty Circle Arc.