Board Thread:News and Announcements/@comment-4698889-20180724122634/@comment-181.66.27.38-20180906233252

Redladydeath wrote: About that, I've been wondering where Kaidor is confirmed to be a Kaito character? I thought the only way to glean if a character is played by a Vocaloid is if they get to sing or have a facial illustration, and Kaidor hasn't done either.

However, the novels don't mention that Allen was identical to a young Arth.

So, the only reason is that Ichika based Arth's design in an Adult Len. I don't think that's enough to say he is a Len character.