I’d really like to see them celebrate Valentine’s day together. Could be in immortal canon, could be a mortal AU. Maybe they have longstanding Valentine's plans they stick to every year? Maybe one of them forgets about the holiday and is blindsided at the last second? Maybe the relationship is New™ and neither are sure how far to take things? Up to you! I just want some Nile/Book Valentine's fluff, please and thank you!