Imagine if this played out differently. Rinko gets caught up in trying to make her family get along and ends up spending two and a half days mediating between them. Finally she manages to convince her parents to accept her sister's relationship, but as she's leaving in the afternoon of the last day she realizes she completely forgot to call Arase. So to make up for it, she stops by his apartment on her way home. When she gets there, she knocks and calls him for a couple minutes before unlocking the door herself and finding him freezing, starved, and barely alive. After briefly panicking and crying out to him, she goes to check and see if he's still alive. Once she realizes his state, her instincts kick in and she carries him to her car and races to the hospital. Once there Rinko brings him inside, gathering her strength from adrenaline and being soley driven by the thought of protecting Arase. He's quickly put onto a gurney and rushed to a room. The doctors tell her to stay in the waiting room while they assess his condition and try to get him stable. She sits there, bawling and cursing herself for not checking on him sooner. Eventually what seems like many hours to her pass before a doctor comes and tells her Arase's in a stable condition and that he's resting now. Relieved, she asks the doctor what his room number is and if she can stay in there. He leads her to the room, and says he'll be back to check on Arase in a few hours. She walks over to his bed and grabs his hand, profusely apologizing and breaking into tears that it's all her fault. Rinko slumps down into the chair near his bed and watches him sleep peacefully for a little bit, before she inevitably falls asleep as well. Hours later, she wakes up to see him up and eating some food while watching her sleep. She jumps up and hugs him, exclaiming about how worried she was. He calmly comforts her, saying he's okay and that she doesn't need to worry anymore. Still concerned, she shyly offers to feed him, to which he happily agrees to. After he's released a couple days later, Rinko demands that he stay at her house while recovering since he had no power and should be somewhere she can help take care of him. He teases her about her just wanting to bring him home to her place, but obviously still agrees to it. For the next couple days she goes to work each morning, and anxiously waits for the days to end so she can go see him. Being his teacher still, she makes sure to bring him the worksheets from each of those days, but doesn't dote on him about doing them, as she tells him that his health comes even before school. In the evenings she makes dinner for the two of them, and at night she tucks him into bed while he jokingly tries to get her to sleep with him for the night. After he's fully recuperated, she pays Arase's electric bill and sends him home with some food, whilst denying his requests to stay longer. Later on, whenever those days were looked back upon, they only ever remember it as a happy memory of when they really got to act like a couple together for the first time.
Edit: didn't mean for this to be so long. I intended for it to end when she feeds him, but I got carried away and wrote the rest too.