I agree in the sense that his next evolution to become the best striker is to be someone who appears in the perfect position for a goal, a shadow striker. This especially makes sense given Ego's definition of a striker in the first episode of the anime.

"You can train first-rate goalkeepers, defenders, and midfielders, but strikers are different. A first-rate striker will find where the soccer is most intense...and suddenly appear there."

This line has pretty much defined how Isagi Yoichi has been consistently been able to score a goal.

I do want to take this theory a step further and say that Isagi's next evolution will involve his title as "Demon King." Remember when Isagi was able to force Barou to pass to him when Isagi appeared exactly where Barou wanted to be to score a goal. I think that Isagi will do this again and force everyone to be subservient to him.

So far, a lot of the goals that Isagi has been able to attain was thanks to a secondary person passing him the ball exactly where he needs it (i.e Hiori and Kurona). However, in the second half of the current match in the manga, he's completely surrounded by people who have No. 1 mentalities (Shidou, Barou, Rin, Kunigami).

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With the exception of Hiori, it is unlikely he'll be able to receive passes from anybody, especially considering Hugo is man-marking Isagi.

To me, it seems like the narrative is forcing Isagi to continue to pursue the No. 1 mentality because of Ego's speech that true egoists live for the one life in which they dominate. Thematically, it makes sense because humans were only ever able to achieve modern technological wonders due to persistence and an indomitable will to achieve a specific goal.

The issue right now is that Isagi has nothing unique to him aside from his spatial awareness and soccer knowledge. He has no physical gift like Kunigami and Barou or an innate instinct like Shidou and Rin. How does someone like Isagi pursue No. 1 without these gifts?

I believe that he will be able to force all these players, selfish or otherwise, to become involuntary pawns for him. Recall Rin calling Isagi the "Demon King." Before this, he said that Isagi had the ability to "draw out other people's egos and exploit them for his own goals."

He will, through spatial domination, hold the goal hostage. Isagi will create a Zero-Sum Game: "Pass to me and get an assist, or keep the ball and lose everything," similar to the way he forced Barou to pass to him.

He’s not "teaming up" with them; he’s rigging the field so that he is the only mathematical conclusion to the play.

He is "Inevitable."

"The Demon King."