My Seatmate Tries to Make Me Fall in Love with Her by Teasing Me Repeatedly, but Somehow She Was the One Who Fell - Chapter 9: Neighbor Seat Phobia

However, he did not know that he was not raising just a harmless pet, but a biological weapon secretly made by the government… a real monster.

As a former librarian, Rand felt that he had been living an ordinary life, the one that he had reclaimed unconsciously every single day.

Recently, he has been a little upset because the pet fish he accidently brought home to raised seems to have undergo some strange changes

Well, it turned into a merman.

- Description from Novelupdates

Inexplicably reborn in the year 2003, having failed terribly in his previous life, the prevailing concern with Xu Tingsheng, that stands above all else, is none other than her. But alas, he is just months away from entering university, while she is but in her first year of junior high… Regarding this, all he can do is wait silently…for now.

Xu Yiyang, who was only late in his life when he was middle-aged, returned to 1999 in a dream.

At the turn of the millennium and the turn of the century, he realized a truth:
Not only to be famous early, to start a business and make money, but also early!
………………
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- Description from Uukanshu

What the heck? She, a famous doctor from the 23rd century, turned into a village peasant girl of a different world!