Board Thread:General Discussion/@comment-73.2.245.207-20170222012536/@comment-24.176.2.221-20170222030252

I don't think this theory is very well substantiated, to be blunt--the lines you're mentioning as having a connection with each other are incredibly vague connections at best. Mothy is usually very straightforward about his foreshadowing and his reveals, often to the point where he'll repeat lyrics word for word to make sure that people get the reference he's making.

Since you mentioned you're a little behind on EC, here's things from elsewhere in the series explicitly related to the boy in Re_Birthday and the girl in Clockwork Lullaby, presented separately.

Re_Birthday:

-Cloture of Yellow, from Allen's perspective, features many references to the song, such as mentioning at one point that he's "unable to see or hear anything, shivering alone in the darkness".

-Cappriccio Farce features a Len character named Irregular who is described as being in the Master of the Court's womb. This character is depicted as wearing Allen's clothing with red and blue chains on his limbs like the ones in Re_Birthday.

-This character, Irregular, shows up as a separate person from Allen in Seven Crimes and Punishments.

-Allen is referred to as "Irregular" by several characters through the series, including in bonus stories and Cloture of Yellow.

-Master of the Court's song mentions her singing a lullaby for Irregular to calm him.

Clockwork Lullaby:

-The song Wordplay quotes Clockwork Lullaby (hence why people assume they're the same character).

-The song Full Moon Laboratory features the same image of the girl in Clockwork Lullaby, as well as the "la la la la lu lu lu" theme. It also talks about how it's her turn to "teach a new song" (hence people assuming it's the same girl here as well).

-The Song That I Heard Somewhere, about Irina's transformation into the Red Cat Mage, explicitly references several lines in Full Moon Laboratory as relating to Irina and her work.

-In the Judgment of Corruption novel, a location is introduced called "Lunaca Labora", where Irina was said to have been put in her red cat body. The name is explained by other characters to translate into "Full Moon Laboratory".

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While there's nothing concrete yet, and a lot of conflicting information on who these people actually are, with all this in mind I don't see anything that really connects the two of them. The Len in Re_Birthday and the Rin in Clockwork Lullaby seem to be indicated to be entirely unrelated people.