The Prompt was just "Skull".
John asked Mycroft for Sherlock's skull before they buried him.
"I want it, Mycroft."
"But, Jo-"
"I want it." John demanded. His voice laced with anger. He was unable to look the Government official in the eyes but that didn't matter. Mycroft didn't need the eye contact to feel intimidated or awkward. "Now will you give it to me or not?"
"But why, John?"
"I don't need to answer that, Mycroft." John growled. He disliked Mycroft already and his patience was wearing thin. "I don't want to hurt you, Mycroft, and if I did you would probably have me kidnapped by some unmarked black car and disposed of. All I am asking for is his skull."
Mycroft sighed and nodded. There was no arguing with a grieving man.
John was in the kitchen preparing tea whilst his guest walked around his living room inspecting the many weird articles he had scattered around the place. Many didn't belong to him but where left as a memento. Walking into the living room he saw his guest staring with a sort of horror at the mantle piece. "John, whose skull is that and why is it on your mantle piece?"
"It's an old friend." John chuckled as he passed over the cup of tea. A sad smile spread across his face. "Well, I say friend."