I mean, it might be kind of a joke, but she's also 100% serious. She'll do it if he requested it.
If Master texted her with "Hey Sasha, I had a manga idea. Please go fuck the black exchange student from the basketball team and send me the video". She would gleefully comply.
Also I am not pulling that student description out of my ass, it was literally from a post Hagu made several weeks ago.
https://x.com/hughuginfo/status/1899175889142964505
Oh yeah, I'm sure she would gleefully comply, especially for reasons involving Master. She kind of says that in chapter 49, with the dudes at the beach, she had totally silly intentions, but when Master got Grumpy about it, she just said 'well, if you need it for your manga, then sure'. Chapter 49 is probably also way after Master is already her favorite guy (if i had to guess that would've happened either Chapter 30, or if it's after that I'd guess Chapter 37 or 38, shorty was yearning bad), and that's a decent bit before they went all the way.
It's a win-win for her, She knows it pushes his buttons and she finds that cute so she'll tease him about it all day long, but if he were to earnestly need it for 'research' she'd do it for that goal, sex feeling good is secondary or lower at that point.
I think that's part of the conceit around the threesome at all. Sasha suggested the threesome to Sanada, she probably also suggested master as the third (she would not have suggested someone else, in earnest, not to Sanada at least), and in chapter 73, her first explanation to Aoi was "they said yes and one of master's favorite manga has one in it, so it's research" before Aoi talks about actually considering his emotions.
She has this effect on him without having sex in 49 + 50 by sending him just a handful of pictures with dudes in it, with nothing indicating if these people were partners ever.
That makes it a win-win for master too? It is a much less compelling win-win. He probably doesn't want to request her having sex with someone for research, but the teasing itself gets ideas in his head anyways, and he's seen enough of Sasha and the tapes that already exist to probably draw whatever (he drew through the pain of having delusional thoughts of Sanada taking Sasha from him, he has the imagination now, did the same thing in chapter 50). But ya know, if he actually was in a situation where he asked, he'd come away from it with the reference material at least? If he was involved and asked maybe he won't have bags under his eyes for 5 chapters like after 65, lmao. It's pretty easy to desexualize sex. People in sex work industries often have long and loving relationships with other people in the industry. if it's all for the manga, it's all for the business bay-bee.