Izuku Midoriya was far from being an idiot, he has been analyzing Quirks since he is a toddler. However, one particular Quirk brought up a serious question again and again since he met with Shoto Todoroki, youngest son of Endeavor, the Flame Hero: Is his Quirk is, Half-Cold Half-Hot is practically perfect, then how is that possible?

He knew that the bi-color haired teen had older siblings, one known to die in an accident where their weak resistance to fire combined with the very strong flames they could make, he knew about his older sister was a teacher with a strong ice Quirk and another older brother with similarly powerful ice powers.

This was like an unbeatable paradox to the smart greenette until he realized one very important thing: Quirk Reproduction Rule Six. This means if two children are twins and the older born with a new Quirk, the younger replicates it or tries to replicate it.

It was a day after their Provisional Hero License Exam which everyone passed because Midoriya could make both Todoroki and that Yoarashi boy to team up peacefully against Gang Orca and his Sidekicks.

The Class 1-A was in its dorms and the One For All's owner sat on the couch in the living room of it, next to him sat the reading Shoto.

"Hey Todoroki-kun?" the dual powered Quirk's wielder looked up to see his caller, the closely sitting Izuku Midoriya, his first friend.

"Yes? What is it?" asked him Endeavor's son, he had no idea what the greenette wanted, plus the latter's determinate look and voice took up the nearby Bakugo's curiosity too.

"Do you have a younger or an older twin sibling?" asked back Izuku from the stoic teen.

"Pardon?" now the asked was surprised.

"Don't be stupid nerd!" shouted the now 'exploded' blond.

"That's a quite specific question does you know?" exclaimed the 'chimera'.

"You Quirk is just too balanced, too perfect. It would be extremely rare to you being an only child from a birth to have it. If it older, you refined the Quirk. If it younger, you were lucky to create this Quirk and they tried to replicate it. Quirks' manifestation might be affected by us around the age of Quirk Manifestation. However, their DNA is formed as the child is grows before birth. Ergo, you made your Quirk. Which is also means it your power. But you must have a twin sibling to balance it out. A twin, who either made the Quirk or replicated it imperfectly." explained the greenette as the others thought on the matter.

"That's sound logical." commented the thinking Katsuki Bakugo.

"I'll ask father and mother about it tomorrow." spoke Shoto.

"You better do ASAP Half and Half." barked the blond.

"Kacchan!" cried Midoriya as the Todoroki started to call his father on phone.