[Omnikaiser]

After watching with subs :

So there is something about Kento. He says what happened 15 years ago was his fault and he should be to blame. And touma would be better not knowing.
and when Sophia answers, instead of saying something like "it's not your fault" like you would normally expect, she says "don't take the blame entirely" implying it is INDEED at least part Kento's fault, plus she adds Calibur is Kento's ... without finishing.

Either Calibur is a family member of Kento, or maybe he is some kind of teacher.
Like Calibur and former Brave would be tutors training kids to be next seiken holders : Kento and Touma. Something like that.
But then Kento did something probably forbidden out of curiosity, maybe enter the book of ancients room or something (he is based on aladdin right ? king of thieves lol) which caused Calibur to be able to gain access to it etc...


EDIT : Just thinking about it. Daishinji first appearance is kinda lame. The character appears for the first time in the background and is like almost useless like he is scenery only.