Hiren
Not actually incest, just pseudo-incest. Didn’t like the way the first couple ended, it was like there was a magical fix and the top got the bottom suddenly. Ugh. As for the second couple, it was good.
Unfather
Hot! Love the twisted obsession. But the ending was a bit... :/
The Devil
Check this out! Note: it’s pseudo-incest, these two aren’t actually twins (one is a demon? Idk) Wait for it to be complete. As of 2021, the novel was 200+ chapters and ongoing. Don’t want to read of ending is tragedy
Miscreants And Mayhem
I Reincarnated as the Little Sister of a Death Game's Murder Mastermind and Failed
Webnovel spoilers: This topic may contain spoiler Basically Makoto stopped seeing Mai as his little sister and grows full on lowkey yandere but definitely possessive. Mai too would stop seeing Makoto as her brother but likes him as a man instead. I think around 10 days or a week or maybe even one day? before the 'D-Day' of the scenario where 'Makoto will murder his friends', they will go to an amusement park in some kind of date-esque scene and ride the Ferris wheel together where Mai asks that they should go to amusement park together again soon, maybe even tomorrow or something (a scheme to stop Makoto from murder).
Momoiro Shoukougun