Library of Ruina predicted Index Nursefather (Limbus Canto IX and Ruina SOTC references)

Equal parts speculation and spoiler about our favorite heretic, Rien.
There's a line in "Children of the City that never quite felt right for the Index in Limbus.

"Now it's time for another vendetta
Going through the shelves
Picking out my pre-written persona"

While this seemingly implies Yan, who was manipulated by the Will of the City, I find the connection rather flimsy. The Index proxies of Ruina have very distinct personalities, with no apparent prescripts that modify them. Further, Yan is explicitly not having his personality dictated by the prescripts, else he would have known before the big reveal at the end of his arc. While his actions were prewritten, his personality was his until the end... at which point he had no personality at all.

However, enter Rien. Bootleg Black Silence. Who was explicitly told by the prescripts to copy Roland's whole flow, bar for bar. He went through the shelves (copied a librarian) for a pre-written persona. And as a bonus? The song includes:

"In thirty minutes find a groom or bride/
Bonus if brunette/
In 90 hours spill their insides"

While not identical, this matches Rien's experience with the prescripts as well - demanding he take a family and then, after finding happiness, watch them die.

Perhaps large speculation, but the coincidence makes me wonder if the character was floated for Ruina and he simply didn't make the cut (possibly as a SOTC enemy to foreshadow Black Silence reveal) before being refined later. If not this, then at the very least they had already considered the possibility of such a person existing.