They have to do this similar to the fight between MCU Peter and Raimiverse Goblin in No Way Home. And their final fight has to happen to at the Sekai Takai. Because all roads lead to this. 

So. We’ll start with Demetri and Eli. They’re talking one night after training about how far they’ve come since Season One. About how they’re not the bullied geeks anymore. Demetri mentions that Kyler hasn’t changed, Eli says guys like him never do. 

Eli looks Demetri deep in the eyes and says one word: “Sorry”. Demetri says “For what?” And Eli responds with “For what I became when I joined Cobra Kai. For what I did to you…for all of it”. Demetri then experiences a quick flashback to everything Eli did to him as the Hawk. Eli asks him if he’s okay, Demetri snaps out of it and says yeah. This is show us that Demetri still has trauma from the events of Seasons 2 & 3. 

Later on, at the high school, Demetri is with Yasmine when Kyler sees them and taunts Demetri about Yas only dating him out of pity. Yas yells at Kyler and he leaves, but Demetri has another flashback to all the times Yas was mean to him in the past, but hides it from her and walks off. 

The remaining Cobra Kai kids, now led by Kyler, who has gone deeper into the dark side, start a fight with the Miyagi Fang kids. The Miyagi Fang kids go to the Cobra Kai Dojo. Kyler taunts Demetri and Demetri loses it. They fight. At first the fight is even. But Kyler continues to taunt, and Demetri’s rage continues to grow. We see a short flashback to an instance of bullying from before the show began. 

Kyler throws a foot, Demetri catches it and incapacitates the foot. This is when the fight becomes like the one from No Way Home. Demetri gets lost in his rage. He just starts beating Kyler. Like really beating him. Fist after fist after fist after fist. Each time Demetri grunts with rage. Kyler tries to fight back, Demetri flips him over and then pulls Kyler to him and then sends him flying to the ground with a kick. Eli watches this, and realises that the very thing that happened to him is now happening to Demetri. The rage is becoming him. 

Everything slows as Demetri slowly walks over to Kyler as Kyler struggles to his knees. Demetri grabs a blade from the wall and screams with rage as he goes to plunge it into Kyler’s chest. As Demetri plunged the blade down, Eli dives in between Demetri and Kyler, catching the blade with both hands. 

Now it becomes a stare down between Demetri and Eli. Demetri grunts with rage as he tries to plunge the blade downwards. Eli stares deep into his eyes. Trying to tell him “Don’t make my mistake”. And just as Demetri falters, we hear a stabbing noise. 

Demetri and Eli look down and see a blade protruding through the bottom of Eli’s torso. Eli falls to the ground, not dead, but badly injured. Kyler grins evilly. Demetri spin kicks him. Knocking him out. Demetri helps Eli, all the while wondering why it felt so good to use the rage. 

As Eli recovers, he knows what he has to do help Demetri. He has to help him hone that rage. So, as Season 6 develops, Eli will help Demetri develop his own rage persona. Demetri will create The Eagle. It’s like Eli’s Hawk, except Demetri has more control over it from the start, whilst Eli claws his way back to badassery in time for his own fight at the Sekai Takai. 

Now we come to the Sekai Takai. It’s time for Demetri and Kyler’s final fight. At first the fight is even, but Demetri holds back a little. Eli encourages Demetri from the sidelines. Kyler temporarily takes the lead in the fight, and he says something disgusting about Yasmine. This makes Demetri lose it all over again. 

Demetri over powers Kyler and starts beating him again. A flurry of fists and kicks. Kyler is now very bloodied up. Demetri keeps on beating the shit out of Kyler as the music slows to a gothic and deathly hum like the No Way Home music from the Peter/Goblin fight scene. As Demetri grunts with rage, Eli watches and realises that Demetri is giving into the rage again. 

And he realises that he is the only one who can save Demetri from the rage. As Demetri goes to deliver another blow to Kyler, Eli steps in. Demetri yells at Eli “What are you doing?! Let me finish him. Let me end him for what he did to us. He deserves it”. Eli says “Look at him! You’ve already given him what he deserves! You’ve won the fight, but it isn’t enough is it? It wasn’t enough for me when I beat Brucks. I had to really beat him bloody, you know. I thought it helped me get the rage out. But it didn’t, it just made me more like them. And that’s what you’re becoming if you keep beating on Kyler, not showing mercy. You’ll be just like them” Eli says, as he catches Demetri’s fist. 

“Don’t make me fight you, Demetri” Eli says. “You’re protecting the bully, Eli! You’re on his side again!” Demetri says. “I’m trying to save you from the rage. Before it destroys you the way it destroyed me. I let the rage in, and it made me lose who I was. I hurt everyone I loved…” Eli says, he grabs Demetri, hands on his neck, tender. “I hate myself most for what I did to you. My binary brother” Eli says. 

All of this, becomes too much for Demetri to handle. He screams and kicks Eli, sending him flying. Eli gets up and assumes fighting position. Because now, the fight stops being about Demetri’s rage vs Kyler. 

The fight becomes Demetri’s rage vs Eli’s regret. 

The fight is bitter, emotional. It’s rage vs regret. It’s angry and tense. Demetri’s putting all his anger, hate and rage into his moves. Eli using his newfound balance to counter Demetri at every turn. Eventually they come into a lock with each other. “Stop. I don’t want hurt you” Eli says. “You’ve already hurt me. This is me hurting you back. How does it feel?” Demetri says. 

Eli tears up. “I hate myself for what I’ve done to you. You were the only one. The only one who stood by me when I fell. The only one who ever helped me get back up. Even when I pushed you away. You never gave up. You saved me. So now it’s my turn. I won’t let you fall. I won’t let you become me. You’re better..” Eli says. 

Eli kicks Demetri, sending him backwards. The very even contest resumes as they fight hard, experiencing flashbacks to all they’ve been through on the show as Demetri becomes the Eagle and Eli becomes the Hawk, meaning we hear Eagle and Hawk sound effects. They counter everything they throw at each other. It’s the fastest, most brutal, most epic fight we’ve ever seen in the show. 

They lock again as Demetri goes for a final blow. Eli holds him in the lock. “Demetri! Remember when the Tenth Doctor regenerated into the eleventh. We cried for days. Please remember that! Remember who you are!” Eli says. Demetri begins to remember some nerdy moments between him and Eli in the form of flashbacks to their childhood. “Remember what we said to each other when we won the science fair we got paired up for when we first met. What did we say to each other!” Eli says. 

We flashback to that day. Young Demetri hugs Eli when they win. “You’re my best friend, Eli!” Young Demetri says. “You’re my best friend too, Demetri!” Young Eli says. Flash back to the present. Demetri, still rageful and still angry. “You’re my best friend!” He says angrily. Then, he falters and the rage washes away. “You’re my best friend, Eli” he says. “I’m sorry for what I did to you. I should never have hurt you. Said those things” Eli says. 

Demetri grabs him and hugs him. “None of that matters now, Eli. You’re my friend” Demetri says. “Best friend” Eli says. “Best friend” Demetri repeats.