Tenko knew Katsuki had always been a rough kid with a smart ass mouth and the pride of someone much taller than him

There's no "but" to that sentence. Tenko thought the kid was bad news, but, much to his annoyance, his little brother Izuku seemed to look past these obvious flaws and followed Katsuki along with his other lackies

"Kacchan is amazing!" Izuku would say both to Tenko and to Katsuki's face. Tenko swears he saw Katsuki's head get bigger after the praise.

You'd think that having a friend like Izuku following you around would garner some special treatment. That Katsuki would see Izuku as his BEST friend, much like how Izuku says they are

You. Would. Think.

But no. Katsuki was all too eager to put down Tenko's baby brother just to make himself seem better. And no matter what Tenko tells Izuku or their mom, Izuku was all too eager to defend his friend and sing his praises

Tenko gave up at a certain point. They were basically babies. Surely one day, Izuku would grow out of it, so Tenko stopped interfering

That was, until Katsuki started getting more physical

All it took was one shove, and Tenko came marching over to set things straight. He didn't care that his mom would probably be disappointed in him for using his quirk like this, but at least all he was doing was lifting Katsuki up and away from his brother

and hitting him

In Tenko's defence, Katsuki threw an explosion at him first

Through the whole little fight, though, Tenko managed to get Katsuki to yell out what was bothering him and why he was being such an ass. Which led to Izuku crying out about how he "Never looked down on Kacchan! Not ever!" and how "I want to be a hero and save people by Kacchan's side!" all while he cried rivers

Which led to even MORE yelling and thrashing from Katsuki. Tenko had to fly the blond home to tell on him to Auntie Mitsuki, with Izuku running after them

THAT got Katsuki to quiet down real quick

In the end, their moms all got together for lunch to talk about what happened

Katsuki huffed and puffed through the whole thing, but did apologize (after a lot of yelling between him and Auntie Mitsuki), and both Tenko's mom and baby brother seemed all too happy to get things resolved (Much to Tenko's confusion and annoyance)

Not much has changed after that

Katsuki was still a cocky little runt, and Izuku still followed him around with stars in his eyes

Tenko thinks their friendship is weird. Always will

But after watching Katsuki beat up a bunch of older kids to defend Izuku, Tenko doesn't think the kid is all that bad