One night in an old abandoned Bunker where a cult was living inside of it and Hinata, Sakura and Naruto were dispatched there to investigate and they were nearly Immediately ambushed by the cultists and Hinata was running for her life across the hall until she tripped over a cord but ignored it and kept on running. as she ran she was cornered with the others surrounded by several cultists and as they surrounded them the cultists separated the others from Hinata and as a cultist slowly walked up with a long, curved, rusty, bloodstained blade and said
"You shall Pay for your sins by dying for our demons in HELL!"
and as he threw the blade over her she closed her eyes for her fate but instead she heard the loud sound of metal clanking together and a large group of gasps and as she looked up she screamed in her head as she saw a massive 8 foot tall man with tattoo's all over the top half of his body and the lower half is covered by robes and an even has a large rusty right triangle-shaped pyramid stuck on his head with chains wrapped around it and he was making loud grunting and gurgling sounds as he stared down the cultist. He then turned to Hinata and Pounded his chest twice before pointing at her which was the universal sign for "I owe you one" which confused the Young Heiress because what would he owe her for? but before she can think about it the man threw the cultist across the room and screamed at the other cultists which they did not listen to and charged.
The man took his massive steak knife shaped great sword and started slashing the Cultists in half in the torso and in many sperate pieces throwing blood everywhere even onto Sakura which made her a little sick as of course there was blood all over he body. The last cultist tried running away but the man grabbed his trusty meat hook and threw it onto the cultists back and stabbed him with blood gushing everywhere and he dragged with the cultist begging for dear life but the man didn't listen and instead ripped his cloak off and then ripped every last inch of skin from his flesh and bone killing him immediately. He then sniffed the Skin like a low-grade drug and walked over to Hinata.
She was still screaming in the head from the whole experience. The man then stabbed his sword into the ground and offered without words to help Hinata off the ground. and as she was helped off the ground Naruto and Sakura ran to her which he responded by Pulling his sword out on him and threatening them to back away without words of course.
"Don't worry they're my friends!" the young heiress explained
As soon as she said that The Man dropped his weapon and gave his hand out asking for a handshake which they frightenedly shook hands for and Sakura frightenedly asked
"W-What is your N-Name?"
He wiped some blood off of Sakura's clothes and started writing on the wall and what he wrote was two drawings. One of a pyramid and one of a head. and Naruto asked him in the politest way possible as so not to tick him off
"So your name is Pyramid Head?"
He only nodded yes
1 hour later...
They had to sneak Pyramid head into the city where they can show him to the Tsunade and the Hokanage. as they walked into her office they told her not to freak out at which they had found. she did not seem scared by what they said until Pyramid head started walking in where the leader herself fell out of her chair in fear and her guards pulled out their daggers and swords at him. He only sighed with the tiredness of how people react to him and he pulled out his massive rusty bloodstained blade and that was enough to scare all the guards enough to drop all of their weapons.
"Don't worry he won't hurt anyone as long as they don't hurt Hinata" proclaimed Naruto which Tsunade gave him a confused face as to why he would protect her of all people. He took a bottle of Ink from Her desk and poured it all over the wooden floor and then painted a diagram with his hands on the wall of something terrifying and also explains a lot.
He was a man, demon or something that was summoned by the cultists but he fought back against them since he realized their demonic ways and in retaliation, they put him in a torture machine where they hooked up meat hooks to his flesh and the more he struggled the more it tore at his flesh. it lasted for who knows how long until Hinata tripped on the cord and shut down the machine and as he removed the Hooks from his flesh he saw Hinata running past him out of sight and he knew that he owed her one hell of a life debt and he won't go until he believes he fulfills the said Life debt. They basically did not know what to do with him so they had decided that he would be living with Hinata at the time being because he won't leave her out of his sight.