Even the guy accompanying Soy Sauce Lady on p.5 swooned at that smile.
It's fortunate that Nao's a kind and good person underneath the barbed exterior because he'd be dangerous if he went the asshole playboy route in life.
That said - I think it's totally fine if Sena just wants to be spoiled, even if the one spoiler her is 5 years her junior. Part of her whole deal is that she had to grow up at age 8 and had a super fragmented family situation that culminated in the brief mother figure in her stepmom passing out of her life all too quickly.
It's very believable and I'd argue understandable that someone who lived that sort of life would seek comfort and "the desire to simply rely on another", because she never got to have that portion in her childhood.
The trick is learning to grow through it and not have it become an issue in her future relationships, but given how close she and Nao are and how aware of her entire situation he is, that's a needle that he can thread with her together. And he's someone who is considerate and protective of those important to him, which is another point in his favor from her side of things.