1 Introduction

It's considered taboo for Pro Heroes to have publicly known relationship or even have kids with each other but one particular pair of heroes decided not to abide by that and defy what had been considered taboo. The Number 42 Pro Hero known as Seer and The Number 19 Pro Hero known as Cutting Edge.

Seer's quirk is called Portal which allowed him make portals by connecting certain fabrics of space together and teleporting far distances but only to places he's been to /familiar with. On the other hand, Cutting Edge, her quirk was called String which allows her to freely manipulate strings that each come out of her 10 fingers. She can control how soft or sharp they come but the sharpness depends on how strong her physical strength is.

But behind the scenes their names were Seiya Asagi (Seer) and Rin Asagi (Cutting Edge). They fell in love with each other during their highschool days in UA high and got married before they even became Pro's. They both shared similar ideals and recognizing how capable both their quirks were, they wanted to create a long lasting bloodline of powerful quirk users, generation to generation and be the founding ancestors of a power house family and generate generational wealth.

Although they genuinely loved each other, they both had an everlasting fueling passion when it came to their plan. When the first child was born, the couple were proud of themselves and couldn't wait to see what quirk their baby girl, Mai Asagi would have.

(No this is not the MC. This is his sister)

When the doctor was finally able to determine what the girls quirk was upon turning the age of 4, the parents were not only shocked but worried. Their daughters quirk made them wonder how their daughter was capable of manifesting such a phenomenal quirk. The closest of the two which her quirk resembled was definitely Seiya.

What was Mai's quirk? The doctor would decide to name this new and unheard of quirk, Star Rage. This would allow Mai to add virtual mass to herself without weighing her down but it didn't make her faster or increase tensile strength but it bolsters her physical attack with force equal to the real mass assigned to them.

But this was also dangerous because the Quirk had no drawback or physical restraints. The only drawback to this quirk was death itself as once the user surpasses a certain density threshold, the titanic amounts of mass will condense their body into a black hole.

Although the parents understood how powerful such a quirk was they didn't weild them quirk themselves so they wouldn't know what it feels like to near the limit or properly control the quirk so they decided that they would have to be strict and train their children the moment they find out their quirk.

They knew that Mai should focus on attack speed and speed more than strength as her Quirk could make up for that and then there would be plenty of time in the future to develop strength.

During the time span of Mai doing medium levels of training and exercises at the age of 4, Seiya and Rin wasted no time with the baby making process and 9 months later, Rin would give birth to a son, who looked just like his father. They would name their son Satoru Asagi and just like with their daughter, 4 years had passed and they went to see what Satoru's quirk would be.

(This isn't the main character either. The Main Character has a older brother and sister)

The parents became even more proud of themselves and their desire for power would grow after this fated day. Their son Satoru would possess a quirk called Infinity? It allowed him to bring the concept of infinity into reality allowing him to manipulate and distort the space before him at will.

(Yes, Mai and Satoru quirks are abilities from Jujutsu Kaisen. Also Infinity won't be as OP as how Gojo uses it)

Seiya was happy at having another successfully powerful child that also had a strong resemblance/connection to his Portal quirk. Rin was obviously happy of course but she herself had mixed feelings. She felt like her husband had let their passion turn the love they once had into a shadow and thus led to an affair.

8 year old Mai and 4 year old Satoru would soon have an illegitimate brother born into this world. A brother born of an Affair, The Unwanted Child.