The desperation to have a loved one back can generate a certain madness in some people.
Something similar happened to Dazai; who moved heaven and earth, searched and investigated any indication there may be to bring his dearest friend, Oda, back.
Many say that he who perseveres achieves, which is why Dazai never gave up.
He had already found 'The Book', and had written in it countless times; he had already created multiple parallel universes and had even created the perfect universe (Beast Au). Oda did not die, plus he was happy in that world. And Dazai was able to read everything that happened in the story in the safety of his apartment.
But it was not enough. Osamu wanted more. Even though he sounds selfish, 'Is it so bad to be selfish for once?'
Eventually, an infamous merchant (who claimed to come from 'Agrabah') approached him, sensing the desperate aura from him. The merchant apparently took notice of his suffering, and gave him a dirty old 'magic' lamp. Dazai couldn't disagree much, as the old man immediately disappeared without a trace.
Curious, Dazai rubbed the lamp (already in his apartment), and purple smoke began to come out of it. Suddenly, Osamu had a 'genie in the lamp' in his house.
The genius was called Chuuya Nakahara (something strange that his name is Japanese despite coming from 'Agrabah').
In the end this blessed genius turned out to be obsolete, since his three wishes could not bring the dead to life, kill or make changes to the universe. So Dazai ended up freeing Chuuya from his chains with a single wish (since he considered it inhumane to keep Chuuya locked in that lamp for so long until he finds a 'use' for him).
Chuuya willingly stayed in his apartment, having nowhere else to go despite being a magical being, and therefore, he could leave and do anything.
"For Allah's sake, Osamu. Could you not leave your clothes lying around?! I'm not your fucking servant!"
Chuuya kneels down to pick up the dirty clothes lying on the floor, belonging to a certain lazy mackerel.
With his magic, he organized things, making sure everything was in its place. Meanwhile, he prepared the washing machine to put the dirty clothes in.
With a pair of Dazai's boxers between his teeth (he's never wondered why he's never disliked the scent), Chuuya sorts the clothes by color. "This goes here," he mutters under his breath.
Chuuya clicks his tongue at the thought of his idiot master. "Stupid, stupid bastard. Dirty and lazy."
Two and a half years have passed, and the two are still living together (quite happy, to the surprise of many).
(Dazai can control his Ability in this AU).