beta
Sion ;
Progressed through time with her everytime she dies,
Killed her every time they progressed and he got the powers,
Shows a bit of sense/care in this timeline AND the timeline where she married that abusive hag,
Saved her even though he has no power at this stage,
Hated her because she's the daughter of the Marquis.
Kideon ;
killed slaves (possibly in every timeline),
Fell in love with her at first sight,
Proposed to her,
Seems super narcissistic and egotistical.
My opinion is based on why they killed in the past regressions :
I would argue that Sion is the better pick of the two because he killed her only because she's the daughter of his enemy, but he is not justified in killing her. However, in comparison, he didn't kill her for no reason—it's because she's related to the Marquis. Kideon? He killed 10 sword slaves for no fkin reason, and it looks like it'll be too late for him to change because he's already leaving before FL could say something like "I don't like injustice/prejudice against slaves".
And what if we time skipped 5 years, what if Kideon finds out that Sion is into his "fiance-to-be"? Would that stop him from hating slaves?
Nonetheless, there's too little information about Kideon to say he's the better choice.