In Bookworm, a child's mana 'color' and strength is heavily influenced by the mother since during pregnancy the mother basically channel her mana into the child.
Usually the mother would take a drug that allow them to be influenced by others' mana easier to reduce the chance of her body rejecting the partner's mana.
And before marriage the couple usually exchange an accessory filled with their partner's mana so their body get used to it for similar reason, though at the same time this serve as a sort of test on how compatible are the two's mana (one of Myne's friend commented on how inappropriate her then-fiance is when his accessory was getting overloaded by Myne's mana and breaking down)
Side note: This same drug is used during the memory diving interrogation that results in quite a few...'amusing' moments later on.