I've seen many instances of people slandering Manabu, but I honestly think he had the best setup to be Ayanokouji’s toughest student opponent.
He's not strongest in every category. There are many people who could outclass him in a specific category. But as an overall opponent inside ANHS Manabu is probably the worst matchup for Ayanokouji.
The main reason is because Ayanokouji usually beats people by manipulating the weakness in them.
Ryuen is creative, but his philosophy and overbrutality make him predictable.
Nagumo is powerful, but he wants attention and validation too much.
Yagami is a WR student, but he got completely fumbled by his Ayanokouji obsession.
Sakayanagi was one of the top strategists, but was immature in some ways, and also fixated on Ayanokouji.
Manabu doesn’t really have any weaknesses.
This guy noticed Ayanokouji early. Not after some huge reveal, not after V7, not after watching him destroy Ryuen. Very early on, Manabu already caught that Ayanokouji wasn’t normal
Then in V4.5, Manabu already knows about the island exam and the Rabbit Group result. He knows Class D’s island victory was really because of Ayanokouji, not Suzune. Ayanokouji himself is surprised because Manabu has information that even most teachers supposedly don’t have. That’s not a small feat. It means Manabu had reach, sources, and the ability to read behind the official story.
He also can't be manipulated by a simple threat of violence, like Sakayangi could have been. He has high-level martial arts statements, and in the sports festival relay, Ayanokouji actually chooses to race him seriously. I'm not saying Manabu is faster than Ayanokouji or anything like that. The important part is that Ayanokouji saw Manabu as someone worth testing himself against, even if only for a short moment. That already puts Manabu in a very small group.
And then there’s Nagumo. Manabu graduates from Class A even with Nagumo trying to interfere with him. Yes, Nagumo was limited because they were in different years, so I’m not calling this a clean 1vs7 classes feat. But nevertheless even with Nagumo’s ambition and influence, Manabu still leaves the school as the Class A representative. Nagumo himself basically treats Manabu as the wall he wanted to overcome and admitted that Manabu is better.
That matters because Nagumo is probably the student with the biggest resource pool in the series. If Manabu can hold his position against that kind of political pressure, he is not someone Ayanokouji can just casually move around with a couple of pawns.
The strongest piece of evidence, though, is Ayanokouji’s own reflection. In Y2 V7, he says he is not inferior to Manabu, but if they had been in the same grade and had to fight under school rules, Manabu’s influence and authority could have given him a serious challenge.
That is a crazy statement when you think about it. Ayanokouji doesn’t say that about many people.
Yagami is emotionally unstable against Ayanokouji.
Nagumo is easy to bait.
Ryuen is reckless.
Sakayanagi is too prideful and immature.
Manabu is disciplined. He doesn’t chase attention. He has social authority, physical ability, intelligence, information control, and the respect of people who normally don’t respect anyone. That kind of opponent is tough for Ayanokouji because there is no obvious emotional lever.
Also, about the Suzune stuff, I do think Manabu’s early harsh treatment of her is the one part of his character that feels incosistent compared to how he is portrayed later. I do think it may have been an early Kinugasa writing issue. Early COTE had a lot of characters whose direction clearly wasn’t fully settled yet, and Manabu’s first scenes feel much harsher than the later version of him.
That's why I think Ayanokouji respects Manabu. Ayanokouji easily breaks unstable people. Manabu is the opposite of that, and so far is the only class leader who displayed that.
Btw, I'm not saying he'd win against Ayanokouji or anything like that, but out of all the students in the story he'd be the hardest to beat.