My Genius, Yandere Boss Keeps Tormenting Me

Monsters overran Earth, and with no other choice, the two of them traveled to another world through a time machine.

After a fierce struggle, they returned to Earth.

By then, Earth had been transformed beyond recognition.

Humanity and the monsters had split into two factions and begun an endless conflict...

(I may have misunderstood what "yandere" meant before, so the title should be "The Highly Intelligent Psycho Big Shot Keeps Tormenting Me.")