I Transmigrated into Dragon Ball, and Goku Became My Sidekick

The protagonist wakes up to find himself deep in the mountains. At first, he thinks it's a prank by a friend, but after checking himself over, he realizes things are far more complicated than he imagined. He's barely clothed, and he's even grown a monkey's tail.

He assumes he has transmigrated into an ancient mythological world and become a little monkey demon who has only just learned to take human form.

After confirming this, the protagonist becomes extremely cautious in everything he does and avoids contact with anyone. After all, a powerless demon like him would surely be doomed if a great immortal happened to spot him.

So the protagonist lives carefully in the forest for more than a decade, until one day, when he sees two young men secretly watching a woman bathe. From that moment on, everything changes.

The protagonist quickly recognizes the two young men as the Crane Hermit and the Turtle Hermit in their youth.

Only after confirming their identities does he realize that he hasn't transmigrated into an ancient mythological world, but into the Dragon Ball world!

And since he has a tail, that proves he's a Super Saiyan!