If you pretend that this is not a reincarnation story and MC is not an adult on the inside it's great. Two kids connecting with each other and relationship maturing between them slowly throughout their childhood and their teens.

Alas it's a reincarnation story so whenever something cute or romantic happens my brain interrupts it with "dude is 30 on the inside, that's super icky man". So I can't enjoy it. And the worst part is, reincarnation aspect doesn't really add anything to the story. Story is icky for no reason.

It's about a man, transmigrated into a book with a new identity as the eldest son of the Billhark family named Edgar, and then later by fortunate coincidences he became friends with the still Young Duchess, Ariel. It's hilarious on how he feels abt tht while transmigration thing and it's also amazing to see how fast gets attached to Ariel and takes on the responsibility to protect Ariel and stay by her side as he has promised to Ariel's mother