This actually works. The surreal and absurd aspects of the show are the result of morphine and other drugs he has to take for his pain. Princess Bubblegum is the young nurse that is nice to him, Finn calls her Princess Bubblegum because she dyes her hair pink and is always chewing gum. Several days before he dies, Finn gives her a picture he drew of her as Princess Bubblegum. After he dies, she tapes it to the inside of her locker.

Fiona is his twin sister. The genderswap episode is actually Finn telling his sister about his dreams and Fiona later having a dream based on it. An aspiring writer, she writes his stories down and puts them in a binder for him as a gift. He passes away with it in his arms. Years later, Fiona will write a series of children books based on her brother’s stories and gives him writing credit.

The Ice King is a lonely old man slowly dying of cancer and Gunther is his grandson. At first, he’s indignant over having to share a hospital room with a kid. Finn tries to talk to him, but the old man ignores and acts cold towards him, hence the Ice King. He starts to warm up though after seeing how well Finn and Gunther get along and that even though the former is dying, he still is willing to play with the Ice King’s grandson. When Finn dies, everyone is surprised when the Ice King gets out of his bed, hobbles over to the boy’s bed, holds his hand and cries.

Marceline is sadder. She’s the bassist/vocalist for Finn’s favorite band and when his illness is diagnosed as terminal, Make-A-Wish asks him what he wants, which is to have Marceline sing him his favorite song. She does it, but also hangs out with him for several hours. Afterward, as soon as she leaves his room, she rushes to the nearest bathroom, locks the door and cries. As a result of meeting Finn, Marceline sets aside time every year to visit terminally ill children.

Jake goes to Finn’s funeral and lays beside the casket and every time Finn’s parents take him to visit Finn’s grave, he lays in front of the tombstone. He dies two years later, despite being young. Fiona believes he died of a broken heart, from losing his best friend. Their parents manage to pull some strings and Jake is buried next to Finn.

Goddammit, now I’m sad as fuck.