カイドウの将来を知っている俺は間違いなく達成できる条件を言い渡す、これなら勝手に達成するだろうからカイドウの枷にはならないだろう。
Even if the prince knows that Kaido would do that anyway, there would be readers
who say 'the prince chained Kaido with that promise!'. Then Oda-sensei would tell in a SBS that 'actually Kaido would have done everything he did without that promise, but he'd have died at Onigashima' and the fandom would be shocked by the prince's power.

…今逃げたらお前が危ないだろうが、それにおれは何をやりゃあいい？」
Kaido's silence is very telling... He wants to be free, but he has never been free before, and also this is a person who is showing he cares about him and will surely be punished if he flees...

どうせ二度目の人生だしやりたいことやったもん勝ちだよねと思っているからだ。
The prince was a soul from our world, but at the end of his life he became a true One Piece character...

でも、できれば長生きしてカイドウの活躍に一喜一憂していきたいなと思う。そんなことができるのであればだが。
T.T. HE WANTED TO LIVE AND SEE KAIDO'S EXPLOITS!!!!!!

穴に落ちながら過去回想→絶対に負けないでくれ→こんな所で負けられるか→意識覚醒
The prince becoming Kaido's Tragic Flashback Power Up is CRAZY WORK. The Corazon to his Law, the Kuina to his Zoro...
And Kaido treasuring that memory so much.... I feel bad for him. The prince really showed him rare kindness, did he?

You asked for ideas... So here there are:

- Inspired by another Yume fic in this syosetsu: There is a Devil Fruit user that can summon the dead, but the dead can choose to answer the summon or not. Kaido wants to fight Oden again soooo badly, and thinks that is who he is summoning, but to his shock is the prince who appears. Now Kaido has to deal with emotions he has kept buried for decades and the prince finds himself a zombie.
The prince, running away: I won't stay where I'm not wanted!
Kaido, running after him: Come back here!

- Seraphim AU: The World Government creating a S-Dragon (A Kaido Seraphim) but he is out of control, so they create a S-Prince to control him... Mostly S-Dragon is clingy and the prince is on his third life and baffled about the situation.

- Since Iris Out came out this fic and the song fused together in my head:
まるでこの世界で二人だけみたいだね なんて少しだけ夢をみてしまっただけ = Kaido and the prince met very briefly, but it impacted both their lives
さよなら もう行かなきゃ 何もかも忘れて = The prince saying goodbye to Kaido, because he is going to be executed T.T
錆びたプールに放たれていく金魚 = Kaido (the fish) released from the Vodka Kingdom into the greater world (a rusty pool)
どこにいるの （ここにいるよ） = To me, that whole section is Kaido and the prince (ghost) talking.

Happy New Year!

▲短縮する