It's still up in the air for me who will confess, but I'm actually leaning toward Miyagi with the way things are going now. Or we might see a kind of scene where Miyagi confronts Sendai with the question, straight up asking "Do you want us to be lovers?" and then Sendai will have to answer honestly. I could definitely see a scene where Miyagi asks this, and Sendai returns the question with a "What do you want, Miyagi?" and that causing a big fight.

While I agree that a confession from Miyagi is far more likely. Her asking to be lovers while giving that necklace this early(???) on is simply too hard to imagine. She's still at the stage where she doesn't fully understand and has yet to process that she likes Sendai in that way.

Trivial similarity: the presentation of barley tea to guests in both works.

Probably this is very basic and default in Japanese culture, with the only drama being the fight early on over Sendai's drink. But I hadn't heard of barley tea (mugicha) before living in Japan a few years ago, and it doesn't come up often in fiction. At least not in anime and manga: perhaps it's because drinks are rarely visually distinct, and barley tea is so default that it's not worth highlighting in dialogue (unlike strawberry milk or caramel milk, or even offering coffee). I don't think it came up in the Arioto manga either, but it did in both sets of novels. Pure text format leads to more specific descriptions of some things, i.e. "barley tea, huh she's treating me like a proper guest" vs. simply seeing cups on the tabel