To follow up on this, I was doing some sexiness and love farming while waiting for a reply, and the "couch sprinkler" Fun had the side-effect of giving Yuna 7 Trust. Not sure how/why, as I'd stopped trying to spend time with everyone for Trust after the first couple of times it didn't give anything when raising it was tied to a requirement.
So for anyone who runs into the same problem with it, chase Fun with three women on the couch.
Back into it! Will this be day 2 in a row without going to bed over this game? Maybe.
Sorry for the long delay, I've been sick for the last two weeks and have been focused on catching up to release the new version.
Such a catastrophic bug would mean that no one would be able to move forward and I'd be quick to notice because the riot would be imminent... The point is that it sounds like a case of "overlevel" and although it's technically impossible, maybe you have done something that has caused it. To know if this is a bug due to a bad download of the game for example or due to it being caused when very specific requirements are met... I would need more details and ask you a few questions because I'm checking and there is nothing out of place. Please, if you are still playing and have Discord, join us and send me a DM.
As for the save... It's been a while since I uploaded a save file so you don't have to start over if you don't want to. If you want a game played 100% by you... that's another story. Here is the post with the save file: https://keisi-studio.itch.io/lust-age-nsfw-by-keisi/devlog/614352/v0150base-onwa...
EDIT: Looking further into a save I have for testing early-mid content... Actually, there is a visual bug in Yuna's description (I have to check the rest of the girls) where the description is not shown correctly. It should show the usual "level up to receive a new task" but instead it shows that you have to advance further in your adventure. It's just a visual bug, as you can continue to level up Yuna without problems and still get exp as usual, she levels up, and... the description updates correctly so there should be no softlock.
In any case, I insist that you seem to have produced an "overlevel" because, in that quest, Yuna can't have her trust at lvl 7 (if I understood you correctly).