Hybrid Hero: Saiyaman

Chapter 4 - Saiyan Rage

In the five years since Izuku Midoriya learned about his Saiyan heritage, he and Katsuki have made tremendous gains in their training; But unfortunately, his father hasn't been able to train him with the Ōzaru form due to the danger of the transformation as a little kid compared to a teenager.

In the meantime, the boys have been getting trained in martial arts. With as experienced an officer as Hisashi is, even with primarily being a scout and a scholar, Izuku and Katsuki learn a lot. Most of their training thus far has been in Saiyan combat styles, though the two have enrolled in a nearby martial arts school specializing in an eclectic style for hero hopefuls. Needless to say, the surprise of the instructors and other students when they reacted in sparring matches with completely unknown techniques brought smiles to the pair for days. They're at the top of their academy even without using extraterrestrial combat.

Then came the day for the next step in their training: ki. Hisashi ushered the two boys into his study to speak on the matter. The Saiyan man sighed and brought his hands up to his mouth, mulling his words over before looking at Katsuki.

"I know I've mentioned this before, Katsuki, but it's different now that the day has come. Do you remember when you were still little kids, and I told you and your parents about my heritage?"

Katsuki nodded, his face losing a little color from his nervousness. "Y-yeah, you also said I'd lag behind Izukkun in pure power, right? Does this have to do with that?"

"You're a very bright young man, Katsuki. Never forget that." Hisashi responded with a chuckle, ruffling the smug blonde's hair before returning to his serious demeanor. "Yes, you are correct. The reason isn't as simple, though. Ki is a potent energy, as you have probably learned on your own. It flows through the cosmos, permeating everything, living and non-living. Yet, despite this, and despite many humans being aware of ki's existence, no heroes ever use it. Do you have a guess as to why this is?"

Katsuki and Izuku looked downward in thought before the former came up with a response. "Maybe it's gotta do with quirks? Did quirks make it impossible to use ki?"

Izuku raised a brow and smiled at his friend. "That makes sense to me. Didn't you and Dr. Tsubasa say that my Saiyan genes and my human quirk genes were incompatible, and that's why I only have one and not both?"

Hisashi gave a thumbs-up and flashed a proud smile. "You both are spot on. While ki does still flow through people with quirks, those who possess any sort of quirk genetics at all are unable to use ki. Ki acts as a catalyst and a primary power source for all quirks, dormant and manifested. Because of this, ki cannot be used in a typical manner by a quirk holder. Technically speaking, whenever you use your quirk, you are using ki, but you are using it in the only way you can. Since Izuku possesses zero quirk genetics, he can use ki in a free form just like I can."

The boys nodded as Hisashi continued, immediately turning his attention to Katsuki. "When free, ki's typical expression is through physical enhancement. Focusing on one's ki allows one to use more power than their muscles can produce on their own. Even if you and Izuku have the same physical might, for example, you may be able to break a board with your full power while Izuku, after ki training, could break through a cinder block with his."

"Ki can also be manifested in a direct form through pure energy." Hisashi held out his hand and manifested a small ball of yellow light, awing the kids. "With this form of expression, one can create attacks like balls and beams or weapons like blades from their hands.