Do you think there is a counterculture in your au with how the main culture is hedonism
"HA HA HA LORE TIME!!!"
SPOILER IF YOU DONT WANT SPOILS ABOUT THE ULR STORY
(MENTIONS OF DEATH AND NONCON)
First off, Very good question! And short answer Yes there is one.
So I need to set this up a bit,
Chara like mentioned in the summary timeline the Die well into the young adult life. The reason they died unlike in Undertale (it was never clarified the sickness that caused it) but the Mutation in the monsters magic is and how often they had really unsafe sex the exposure to the mutation magic caused them to get ill and eventually die from it but like mentioned in Undertale Chara left them underground but they never knew Asriel in their life. So explaining their death is in order.
Chara the more the indulged their libido and hunger for pleasure and self satisfaction grew gravely ill from the extensive exposure to the Monster's mutated magic. They didn't immediately get worse how ever they had enough strength to take the souls of several monsters and in a lust driven trance push their way through the barrier and stumble into the village located at the foot of the mountain.
(Just for visuals when suffering from Magic Mutation in Human before they die they go in to this heat like state that makes them crave touch and sex in general before over heating and dying in most cases.)
The Villagers saw Chara and wanted to help them but seeing the state they were in and how Chara tried to (forcefully) take someone in they heated state the Village hesitated to approach them again and eventually Chara subsumed to their sickness and they didn't make it.
Seeing the Lustful state Chara was in and the near forgotten legions of monsters living in the woods. The Villagers made the assumption that Chara was tainted by the monsters in the woods and that their fall into hedonism was the cause. This isn't fully true but the Church that was over the Village saw that capitalizing on this would further their agendas of controlling the village further.
So when the Monster eventually leave the under ground they will have to face the Village and their centuries of practiced Asceticism. Frisk is from the village and given their Aroace they never care much for hedonism until they became bi-curious and joined the more underground LGBTQIA scene to safely explore their identity btu as the story goes they fell down a hole before they got to far.
I will explain the Current Time Village more once it makes more sense.