Financial situations aside, if it's anyone's treat its most definitely Sayu's.
They're just as likely to split the bill among themselves and pay for their own portion though.
edit-actually, reading Fukuhime's latest blog post it definitely sounds like it's Sayu's treat.
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Can I just reiterate how much I already really love this current group?
Each and every one of them have such promising talents, with their own weaknesses just adding to their charming personalities, a very interesting in-group dynamics and lastly, their looks certainly make for a pleasant sight.
... but one thing that recently makes me appreciate and fall even deeper in love with them is how they so adore, respect and in all seriousness doing their best to learn what they can from Sayu.
One of Sakura's latest
blogpost is what drove me to make this post actually. She's not someone I'd expect to write with this kind of deep admiration for Sayu since I've seen so little of them interacting
(same with Zukki actually, can't get a read on her too but then again she seems to be taking her cues more from Aika's school of thought). It looks like something Ayumin or Duu would write

Starting from the obvious like Maachan clinging to her nonstop, the two subleaders hanging on her every word, to coaxing Sayashi out of her shell and encouraging her to be more expressive, to being Ikuta's "bullying" partner teaching her to steel herself and go all out with her character, I honestly feel quite confidently that out of all members in Morning Musume's history, Sayu is the member that directly affects her kouhais the most. Well, during her tenure as the Leader anyhow

Yeah, I'm ultimately just a Sayu fanboy first and foremost and this is probably biased as all hell

but it makes me kinda happy that although Sayu might not have her spotlight in the group for as long as I'd like, I still could see a little bit of her in the remaining members due to her influence and lasting impression on them.