This whole comment! This is literally how I felt about the whole him going back. I mean it sucks either way but in all honesty I only see a future for him with Cauis. I mean it’s sucks that he has to make a decision like either way he’s gonna lose out on something but I think in the end he will be happier with Cauis. The again I’m all for Cauis being able to go to his world but with him being that big I don’t think that would work either
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There’s also this looming issue with him going back that they haven’t revealed yet...like don’t tell me if Cauis doesn’t mate with Kouichi he’s gonna die or something!
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Well... Maybe it wouldn't be so weird if Caius traveled to Kouichi's world... I mean, would he be bigger than Shaquille O'Neal? LMAO
I think the reason he'll die, is because of the prophecy... Remember that they said the future king MUST have his wife by his side, otherwise things could go really wrong?
I think that's what they meant? That if Kouichi were to go back, Caius wouldn't be able to be the king, and then would die because of the power that their "God" gives him?
I understood like that, but I may be wrong...
The prophecy around Caius just states that if he married anyone from Eustil (his world) he will spark a catastrophe (prophecy really seems sketchy at to me though...). Tildant's tradition is that the King or future King must be married and doesn't really have anything to do with the prophecy. Which means Koichi stays and marries him or he summons another Bride or steps out of the line of succession in favor of his brother (since the prophecy only pertains to Caius). But based on many other magic systems coupled with a little common sense and the fact that the summoning magic Caius used to pull Koichi was lost and probably forbidden plus some spoilers I both read and saw there is absolutely no way that he won't pay some kind of price even if the cost isn't Death. I mean he probably searched for and researched the summoning ritual for years amassing the power of several individuals (large scale summonings are typically depicted as a group activity) to use it even if Royal Titans have more magical reserves then the average Titan that still probably a massive energy output...

Why exactly is he going back?
He's definetely going to regret going back...
Even if Caius were to be fine, Kouichi would regret...
His mother will always be dead, with or without him... Kouichi didn't get the point when Caius told him she would die anyway...
I found Kouichi really selfish when he said he wouldn't let his mother "sacrifice" be in vain... I mean... His mother didn't sacrifice anything, she would be pissed off if she was to listen to that...
His mother would die anyway, meaning it was her time and place to die, not the cause... So, when she died while Kouichi was there, she didn't die because of him or something like that... She died because she had to...
Also... About his best friend... Once Kouichi goes back, he's going to be alone... Even if he has his best friend, is not like they'll be together 24 hours a day... His friend will find someone, maybe have kids, follow his own path...
Kouichi was always trying to follow other people's path, he never tried to follow his own...
Saying all that... If this manga has a tragic ending, I'm never, EVER reading something ongoing again! Σ(っ°Д °;)っ