https://www.dlsite.com/books/work/=/product_id/BJ303076.html
https://book.dmm.co.jp/detail/dmmmg_2765/
Since the other version is pretty upscaled.

NTR WARNING

Base +7, MelmothTheWanderer -30, aasp2 +33, Rek_s +6, bigscuba +8, xdddeath +6, riguanghuanling +6, CX~DeribuRa +29, Kiranta +6, Orengestar +7, lololo16 -25, eqpe6p +14

Summary of story as far as i can understand:
2 nieces of male MC see his big hard dick one time they go on hot spring trip together while they are young, they become sluts thanks to that.
some years later(a decade?) MCs brother calls him to "ask" him to take care of the 2 girls since their new school is near his house and hes just bought a big house but still doesnt have wife and kids.
They start living together and the slut nieces pretty much reverse rape him into relationship with them.
Living together with 2 sluts gets pretty exhausting so he asks them to refrain from sex until the exams are over, which they agree to. altough they are still sluts so they fuck the boys of the class behind MCs back(NTR). They have a nice hotspring trip since girls ask that as a price for no sex before exams, during which they explain that what happened there 10(?) years ago made them into such sluts and "made them fall in love with him". After trip MC comes home to hear slut n.1 getting gangbanged, and slut n.2 explains to him whats been going on, and fucks him since he gets hard from listening how they have been cheating on him like the cuck beta he is. From there on its happy life of them "getting married" and then he finds tons of sexvids from the 2 of them NTRing him, masturbates to that, gets caught by the slut n.2 who proceeds to help him masturbate and then goes to fuck one of the men.
The 2 of them then continue NTRing him while sending him vids or calling him while doing so and he happily keeps masturbating as they are stolen.

Base +7, Gitami +12, holabrotato1 -6, eqpe6p +14

Last chapter is a different story, last few pages are ending for 2 nieces one where they send their uncle ntr vids so he will hard fuck them out of jelousy later.

Base +9, ChaseRaph69 +6