MTL - After the Boss Retires, He Becomes Obsessed with Raising Cubs - Chapter 258 Cute love the little mermaid 15...

The protagonist of the collapse of the three former civilizations is Dr. Mei. What is the end of logic, the strongest brain, super intelligence, this is the story of the strongest scientist of Honkai with knowledge of the moon becoming the god of science!

- Description from novelbuddy

Xue Xi is forced to fall in love at first sight with this dangerous man on their first meeting. With death being the only other option, she makes the first move:

When the rifts between worlds opened, countless monsters flooded through, engulfing human cities and plunging the world into chaos. Faced with this apocalyptic crisis, humanity was forced into a new era where every individual had to choose a profession. Nations now compete to cultivate elite practitioners, striving for supremacy in the rankings of alternate world conquests.But as the world teeters on the brink, the first and greatest champion awakens after a million years of slumber—armed with untold buff amassed from his millennia of AFK grinding.The bosses of the otherworld tremble in fear. Global T0-ranked powerhouses bow down, offering their loyalty...[Disclaimer: Here countries fight against each other and this is adapted into a Manhua.][Schedule: 2 Chapters/Day]

Qin Chuan arrived in a parallel world and got bound to a system.