Is a purity run even possible without cheats? The money grind is insane (why can’t we sell stuff? Why can’t we also get items from monsters? Why are items so expensive?) and, unless I just don’t understand the mechanic, it seems like Sana’s invisible lewdness meter just passively builds up. One moment, she’s being timid when surrounded by those guys outside of Garett’s place then the next she’s letting them grope her and getting fucked by random guys. Then there’s also the issue of the unavoidable groping by croc girl. There should be an option to opt out of drinking to avoid that, at least not the point of blacking out.
It’s weird though, on my original playthrough where I wasn’t being careful with Sana (letting her get molested by monsters and triggering events), she stayed in the “exited to meet new people” state until the second town, but even then it took until the scene where you watch her through the window for her to change to the “Sana might have messed up” state. I don’t get it at all. I did less yet it progressed faster. Like literally all it took to level up lewdness on that run attempt was her clothes getting shredded in a fight, not even molested, not even touched once by anyone infact, yet when I let stuff happen to her it took way longer.
The pure run is definitely possible because people have done it before.
There is no real reward for doing a pure run, it's meant as a challenge as you don't even have access to all of Sana's spells.
Regarding Sana's lewd progression, there is a lot of randomness involved depending on what she does during your stay in towns but the fastest way by far is her getting attacked by dungeon monsters.