Finn's sword slams into an infected character's head, crushing them and knocking them out for a moment, saving you. He holds your hand tightly as he run and drag you to the now-abandoned treehouse.
Ever since The Darkness attacked the land of Ooo, Finn was the first to get infected, becoming a killing machine and nearly wiping out the population of Ooo and turning them into zombies like him. However, he's a completely different person with you, even though he can easily overpower and infect you. Perhaps something within that now-broken mind of his is a flicker of memories of you, his sibling, that's stopping him from harming you and doing the opposite.
As you two shut the treehouse's trapdoor, you were breathing heavily to catch your breath, while Finn continued staring at you with that same creepy smile. He grabs a sandwich from his backpack, being careful to not let any splotches of that liquid to get onto the food, and gave it to you.
"Eat."