In the first half, Nasa lets his tendency to get really involved in something get the best of him, and he works on a computer project all day and through the night. When he’s done, he has a fever, and Tsukasa is committed to being the “cute newlywed wife” who sees to his every need until he’s better.
That includes making him food and administering medicine, but also more intimate things like having him strip (as much as he dares to) so she can wipe down his sweat. By the end of the day, he’s feeling much better…better enough to get frisky in bed.
But Tsukasa again warns him to know when to “apply the brakes”—she’ knows he’s still not fully recovered enough for strenuous activity. As for Tsukasa, she drops one last hint about her mysterious origins by declaring she “can’t get sick or hurt”.
The remainder of the episode is actually the reason Nasa worked so hard he got sick: he wanted to be able to go to the summer festival with Tsukasa. He makes what he believes is not an unreasonable request to watch Tsukasa change into the yukata Kaname lent her, and doesn’t forget his camera—mostly to take pictures of his cute wife, not fireworks.
Nasa shows he’s not good at everything when he instantly fails at goldfish scooping, and Tsukasa confesses that the way they made takoyaki at their party is not her favorite way, and she’s super stoked to get the traditional kind at a food stall. Finally the two make and offering and pray for a long and happy marriage, for their health, and for better luck scooping fish in the future.
Then they join the others to watch the fireworks, Nasa looks forward to going to next year’s festival with his wife, and they return home together, husband and wife. Nothing too fancy! Certainly no other further revelations about Tsukasa’s possibly immortal status are revealed.
In this regard, TONIKAWA ends just the way it should have, with the lovely status quo of a happy Nasa and Tsukasa continuing to enjoy their lives with one another and their little circle of friends. It’s simple and mundane, but in the very best way, and I wouldn’t mind more heartwarming comfort food of this kind at some point in the future.