I Turned into an Adorable, Irresistible Darling

Gu Yifan always knew he wasn't very lucky. He muddled through life, and long ago learned to read the room and watch people's expressions when he spoke.

But he never imagined he could be this unlucky. He ran into a home invader, and when he opened his eyes again, he was in another world.

He also seemed to have become a pet. Before Gu Yifan could panic, he began doing his best to please his caretaker so he could survive. Just when he thought he had earned his caretaker's affection, the caretaker said:

"This little male is being raised very well. We can give him away now!"

Gu Yifan: ???

In a daze, Gu Yifan, who thought of himself as a pet, became the Demon King's bonded mate.

A little scene

The Demon King stared at the little thing he'd been given: "So tiny. Looks completely useless!"

The little thing, Gu Yifan, smiled sweetly and carefully hugged his new caretaker's finger.

The Demon King: "Maybe he's a little useful after all. I'll keep him for now."

Important: At the start of his transmigration, the protagonist is a thumb-sized person. Everyone loves him, and he charms them all.

My own worldbuilding is extensive. The protagonist is a rare species whose members are extremely well protected.

Theme: Even a little nobody can achieve great things if they work hard