A/n: Okay, so I found this very wholesome
...
Luke - Big brother, will you like this cookie?
Mammon - ...
You -...
Mammon - Did ya just call me big brother?
Luke (blushes) - What if I did? Also, I just had some extra cookies, okay? Don't get the wrong idea.
Luke shoves the cookie in Mammon's hand and runs away. Mammon stares at the cookie, then at the fading back of Luke, then at you.
Mammon - Uh I have some work to do. Bye.
You don't miss the gentle smile on his face as he stares at the cookie while walking.
Next day
You - Hey Luke, why do you look so worried?
Luke - *sniffle* I don't know how but... I somehow got enough Grimm to buy a house in the Devildom. I don't know what to do with all that money.
Your eyes widen.
Mammon (whistling as he was passing by) (his face blooms into a beautiful smile when he sees the two of you)- Ah human, Fido.
You pat Luke one last time and get up, pulling Mammon with you.
You - Mammon! You can't give all that money to a child.
Mammon (shocked) - 'course I can. *realizing* H-huh? I don't know what ya talking about. What money?
You sigh.