Preface: This will contain spoilers for Blue Lock. I am going to be breaking down characters relationships and overall how I think the characters are being used as story devices in relation to each other. 

So I want to focus on Isagi, Bachira, Nagi, Reo and Rin. Specifically how they relate to each other and how the various relationships (Isagi, Bachira and Rin) (Nagi, Reo and Isagi) foil each other. 

Nagi and Reo

Reo and Nagi had known each other in high school. Reo worked as a catalyst to Nagi. A genius at soccer, but had none of the passion for it. Reo (through bribing him, the perks of being a rich kid) convinced Nagi to join their high school soccer team. The pair was unstoppable together. The pair made a promise to become the best soccer players in the world together.

Their skilled partnership is what landed them in the Blue Lock facility in the first place. Even within Blue Lock the pair had won almost every match against their team, except against Isagi and Team Z. The loss hit them both hard, but mostly Nagi. He saw a challenge in Isagi and the fun in soccer that he didn't understand before. It also was the beginning of the total collapse of his relationship with Reo. 

Isagi and Bachira

Isagi has grown an incredible amount so far in the show. The main catalyst of his growth being Bachira. From the first episode and the first elimination challenge at the Blue Lock facility Bachira was pushing Isagi towards gaining confidence in himself (and finding the egotistical nature that all forwards apparently have.) Bachira gave him the pass and the words of encouragement (no matter how rude or backhanded they sounded) for Isagi to take the shot at the person with the highest rank in their Group Z. After that instance Bachira was basically a crutch for Isagi to find his ego. In every game they played up to the Second Selection Bachira was someone who Isagi was on the same wavelength with. 

After the first trial of the Second Selection, Isagi and Bachira met up and agreed to be in a 3v3 together as per the rules of trial 2. They teamed up with Nagi (we'll get to his deal) and subsequently lost to the Top 3 players, including Rin. The Top 3 took Bachira onto their team forming a team of four (as are the rules of trial 2) and moved onto the next part of the selection.

Second Selection

I wanted to go over the rules of the second trial rules real quickly as they are a core component to how these characters are interacting now. So as players completed the first trial, their rank numbers were revealed. Their rank numbers are the order in which they finished the first trial, ie Rin being the first person to finish the trial and being Rank #1. 

 The rules of second selection are as follows: 

• Created a team of 3 (members are of your choice)
• Play a 3v3 against teams of your choosing. Both teams must agree to the match in order for the match to take place
• First team to 5 points win the match. The winning team choose a member of the losing team to make a teams of four and two. 
• The new team of four moves on to a 4v4 match, winner takes another player to make a team of five and pass Second Selection
• The teams of two play a 2v2 and the winning team takes one member to make a team of three, then return to the 3v3 stage. 
• Players not picked to join a team are eliminated from Blue Lock
• Cycle continues until all players are in a team of five or eliminated

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As our two pairs are each looking for a third player for the next trial, Nagi and Reo ask Isagi to join them and he vehemently refused to leave Bachira. This is where we see the first major divide between Nagi and Reo. 

Nagi had a fascination with Isgai, as he was the reason Nagi has lost for the first time in his life. With his fascination, he decided to join Isagi and Bachira in their 3v3. Nagi saw this as an opportunity to grow as a soccer player. He knew that the only way for him to improve was to grow away from Reo. Nagi recognized the fact that he and Reo were becoming stagnant, especially in the face of all the remarkable players within Blue Lock. 

Reo, felt abandoned since he was the person who discovered Nagi. Reo felt almost as if Nagi belonged to him and couldn't handle the thought of Nagi playing with someone else. The moment Nagi left with Team Isagi he vowed to play and win against Team Isagi and win Nagi back. Unfortunately Team Reo lost to Team Isagi and the fallout was at a head. 

Nagi, in attempts to explain that Team Isagi only won because they knew Reo's skills and were able to rely on Reo's ability to get out of a tough situation and count on that as the basis for their final play. Reo saw his words as pity and in response said:

"You've forgotten our promise that we'd become the best in the world together. If you're going to abandon me, then damn well do it properly."

Nagi takes this personally, in the moment his response is rough. Basically he says that he's past caring what Reo thinks and wants. That he wants to be the best in the world and he won't be able to do that if he's bored in every match he plays with Reo. The conversation ends with Nagi saying: 

"Become the one that chooses, not the one waiting to be chosen."

All that being said lets look at Isagi and Bachira. Isagi and Bachira were THE pair in Team Z and they are split up because someone more skilled (Rin the player currently ranked #1 in Blue Lock) decided to take the person with more natural talent of the pair, Bachira.

Isagi is in the position of Reo, chasing after Bachira in an attempt to win him back from Rin. The biggest difference in their situations right now is that at the start of their relationship Bachira encouraged Isgai to aim for the top, regardless of who he was taking down and climbing over to get there. In addition to that, Bachira and Isagi have a mutual love for soccer and the understanding that they are rivals first and friends/teammates second. 

Now what does this mean for the relationship between Isagi, Bachira, and Rin? Personally at this point I think that Bachira is more of an afterthought for Isagi. Yes, he does want his friend back. Yes, that was his driving force up until now. However, once this final 4v4 started between Team Isagi and Team Rin Isagi's inner monologue has not been focused on Bachira joining his team. Moreso he has been focused on trying to encompass Rin and dominate the field the way Rin is able too. In the first match Isagi played against Rin he got a taste of someone in an entirely different league than he was and wants to devour that power for himself. 

To the audience it seems as though Bachira is even less bothered about this development. He will do whatever he can to have fun playing soccer. He is looking for someone that will "excite his monster". His reason to play soccer is to find someone who will understand him. He wants that person to be Isagi. He wouldn't bother befriending him in the first place if he wasn't intrigued by Isagi in the first place. And now that he is playing with the person who is ranked #1 Bachira is starting to consider if Rin is more compatible "to his monster" because of the larger gap in skill. 

What is to come?

Now the rest of this is going to be fully speculation. Personally I don't think that Bachira is going to be all that interested in Rin for much longer. Rin is too perfect, his skill level is too high for Bachira to be intrested in the game. There won't be any tension or suspense. Through the course of this 4v4 I feel like he's going to see just how much Isagi has grown and once again have it spark interest Isagi. 

I think Isagi will appreciate having Bachira back, Bachira will probably continue to be an inspiration for him to grow in Blue Lock. I think even if Team Isagi loses, he will be more upset about not being able to defeat Rin then he will be separated from Bachira. 

As far as Nagi and Reo go, I think only Reo will be able to fix their relationship. Nagi does truly care about Reo. He says as much in a monologue during the beginning of the 4v4. Neither of them will be able to move on if Reo can't realize that Nagi was holding him back from growing as a forward. 

I'm not totally sure if Nagi and Reo will be able to reconcile. It would make sense thematically if they didn't. Since Bachira and Isagi seem to be going into a more positive direction. Even so, I would like to see all of them be able to at least come to some kind of understanding. 

It would be satisfying too, to see someone actually hit their rock bottom as well. Reo came in as a hotshot genius on Team V with a win streak within Blue Lock of 3-0 before playing against Team Z. Then after having to deal with the defeat, losing his best friend to the person who beat him, then losing against his best friend, and watching the guy who basically replaced him in Nagi's world pass him in the rankings. Especially with his counterpart Isagi being able to move past all his struggles and presumably rise to the top.