I do believe that, in order for the story to develop and reveal that Mana actually did care for Allen and not just Nea, it might be feasible that Mana didn't know that Allen was Nea's host.
But if that's the case it must have been quite a coincidence for Mana and Allen to have gotten acquainted AND for Allen to miraculously have become Nea's host :/
I can't think of any way to explain it though unfortunately XD
I feel like we should be able to say that Mana probably didn't know that Allen was the host based on his pretty extreme confusion and amnesia in Lost Fragments of Snow. He wasn't even aware that his brother was dead, let alone that his memories were stored in a host named Allen. If his memories were intact, the only way he could possibly recognize Red (who wasn't named Allen yet) as the host would be to notice that he looked an awful lot like past!Allen and put two and two together. He might have noticed the resemblance subconsciously - it was probably what caused him to decide Red's name was "Allen" - but he shows no indication of knowing the significance of that name. I grant that he might have had a moment of lucidity not yet portrayed in canon where he put everything together, but we don't have any evidence of that yet as far as I know.
Oh, hey! Remember this?
This page seems to imply that the way Cross was supposed to recognize the host was to find the "Allen" who would at some point "appear in front of Mana." This would be part of the reason for his monitoring of Mana. Maybe some subconscious part of Mana recognized that Red and past!Allen were one and the same and that he needed to change Red's name to Allen so that Cross would know he was the host. It's also possible that Mana's insanity was at least partly obfuscation on his part and that his did this deliberately.
Regarding the 14th's song, if Mana didn't know that Allen was the host, I agree that it gets somewhat sketchy. But maybe it's somewhat less so if the 14th's song has further significance than just being something that Nea wrote to control the Ark. It seems pretty plausible that the song could be something from his and Mana's childhood, maybe taught to them by their mother. In fact, we know that this must be true based on Allen/Nea remembering Mama Campbell singing it over the twins as babies at the end of Night 213. This would explain Mana knowing it as well as Nea and give it a strong sentimental value. Teaching the kid you're fostering a favourite song from your childhood is a lot more likely. If we go with believing that Mana subconscious recognized Allen/Red as the host, then that could have been a factor as well.
Sorry if it seems I've been weighing in too often or too verbosely on this issue lately.
Last edited by KitforKat; July 16, 2014 at 01:14 AM.