Hogwarts is doomed (a harry potter/helluva boss crossover)

Chapter 9- The Choosing.

Asmodeus sighed with relief as he got home. It had been Fizz's idea to try manipulating Lucy by way of bringing up Adam, and it had worked spectacularly. Now, he just had to explain to Harry what a Chosen was and how he had to do the ritual.

Carrying the small child into the living room, he sat him down in the best armchair and sat himself in a chair opposite.

"Now, Harry, I wish for you to become my Chosen. This would mean that you will be able to use demonic magic and rituals and be able to transfer into a demon form -"

"What's a Demon form? And what's a ritual?" Harry asked curiously.

Asmodeus sighed to himself. He should have remembered that Harry was , A- three years old and B- completely unaware of the nuances of Hell beside the fact that it exists. He looked surreptitiously around to see if Via or Loona were going to arrive to help, but when no one appeared, he turned back to Harry.

"OK, so... you are a human. That won't change as such, but you will be able to look like a Demon, potentially like myself, Fizz,"
Who Harry had met and instantly liked at breakfast,
"Loona, Via or Charlie!"

Harry looked very excited at this fact, listening with a lot more interest.

"As well as that, you may  be able to- er, to.. I think it's best if I show you. Do you want to walk or -"
Before he had finished his sentence,  Harry had floated up to sit on his shoulders, giggling delightedly.
He had to blink and rub his eyes before he realised that Harry was, indeed, a wizard. Albeit a very small one but still.

They walked      
                                                    Up
                                             And
                                        Up
                                 And
                           Up
                   And
              Up
      And
Up

Until they reached the window that led to the roof. Harry obligingly ducked as Asmodeus bent through the hole and out onto the wide circular floor  of his  tower, undeneath the lighting. The floor ran around the thin pole from which the next part of the building emerged from, far above their heads. Setting the boy down, he instructed
"Now, stay there and watch very carefully."
Before taking 5 big steps back and releasing his control.
In seconds, he felt his hair turn to a blaze of fire that danced around his face and down his back.
His arms turned to flame-like energy as the twin heads in his fiery mane changed to dragon heads and blew their own dark blue and red flames into the gathering inferno. He grinned at Harry, who looked absolutely gobsmacked, then battled his flames into submission.
Appearing back as his normal self he elaborated:
"Not everyone's is the same; my sister Bee can do something quite similar to mine, Alastor, you remember him, don't you? His antlers turn to dark energy, he gains tentacle-like whips of magic, the air darkens, and his body dislocates. Stolas-"

"The worried owl-person?" Harry interrupted curiously

Asmodeus stifled his laughter quickly "Yes, that's him. He can turn to a sort of owl with  jet-black feathers, huge  wings, jagged teeth, and his eyes glow. Everyone's is different."

"And I'll look like you and Loona-Doggie?"

The Sin wisely chose not to comment on the Doggie bit and nodded. "Yep, you will be a demon like us. However, you will be able to transform into your human form whenever, while we need to use grimoires to do so."

Harry looked very confused.
"What's a grimewor?"

"A grimoire is a magical book that every royal demon or Overlord has, they are written by our ancestors and contain powerful magic and rituals, no-one can read them without our explicit permission. In an Overlord's case, they write their own containing their own rituals and magics."