The Binding of Raijin and Thunderkeg

Thunderkeg asked the storm for rain and got the storm itself. Generations ago the plains beyond the Wailing Mountains dried up, and a good people there starved. Thunderkeg, a plain elementalist, reached for a forbidden spell and called the spirit of the storm down to beg for rain.

Raijin came. The Storm Celestial took the mortal's summons as an insult and scoured the plains bare with wind and flood, and Thunderkeg could not match him, so he cast the one spell a man casts once. He bound their fates together and caged the Celestial inside his own body.

Thunderkeg's endless good humor and Raijin's wild energy fused in that cage into Raijin Thunderkeg, a jovial Celestial who walks the world in flesh, one being where two had been. Inai makes no apology for letting Thunderkeg stumble on that forbidden spell, and Raijin says his brother merely set him loose; he accepts the meddling without forgiving it. Whether Inai ever stood on those plains himself, neither brother says.