You found an Erotic Book (あなたはHな本をみつけた) by Namboku, a two part doujinshi featuring Asgore x Toriel and Alphys x Undyne. English translation and editing by me.
Let me know if you have any comments, questions, or feedback.

Doujinshi Info:
https://www.doujinshi.org/book/939381/
https://www.pixiv.net/en/artworks/58256075

Artist's Pixiv:
https://www.pixiv.net/en/users/34059

Please support the artist by buying their work:
https://namboku.booth.pm/items/312889

RAW/JP: https://e-hentai.org/g/1019576/249142d799/
ZH: https://e-hentai.org/g/1027732/2ea7bbf67e/

I always love to see more Namboku! They are one of my favorite artists to translate. Great work on this one!
The only feedback I might give is adjusting the levels to correct the washed out greys of the scan for a sharper black and white.
You can see the kind of difference leveling makes in the ZH translation you linked.

Thanks again for the hard work!

Base +7, Nenio +13, Jopjop420 +4