Soo the secret special manju is prostitution? (￣∇￣")

Nah, Sei has only does it with Yakihiko. This sex was their first ever sex. The reason the store is popular is because Yakihiko's rich.

but the store isn't Yakihiko's? oh does he influence the store's popularity with his presence only? but that would be more because he is famous rather than just rich...

but still why is the special manju so pricey?! wasn't it 500$? Σ( ￣□￣||)

Japan is a weird place, have you ever heard about the pricey watermelon and melon? They cost 3.2 million yen ($29,000). There's also the case with Koi fish, eel, Bonsai. So it wasn't a surprise to me at all.

Yeah.
So Sei did said in early on that Yakihiko is handsome, popular and smart. So Yakihiko's popularity has something to do with it. But Yakihiko's being rich also add a bonus to his popularity. You know since he's handsome, smart and rich. That would made the most desirable fish amongst people wouldn't he? Besides, Sei and Yakihiko are like those comedy duo, so people could probably also being drawn to their duo.

DA FAK?! Σ( ￣□￣||)

So it's like that. Makes sense...