It’s All Inevitable And All His Fault

It’s all inevitable and all his fault

Chronology of Major Gyjo moments (sources cited)

Gyro refuses to leave Johnny behind despite making it a point that he won't be slowed down by him

Chapter 14 - Across the Arizona Desert: Continuing on the Shortest Route

2) After being attacked, Johnny states the only one he trusts is Gyro

Also, early example of Johnny being willing to give the corpse up to save Gyro (even before Sugar Mountain!)

Chapter 27: Tusk (Part 3)

3) Gyro disobeying his father and familial tradition by giving in to his urge to save Johnny (and thereby fight like a 'true man' for what he wants)

Chapter 35: The True Man's World (Part 3)

4) Gyro putting his faith in Johnny to defeat their attacker. When Johnny thinks he's failed, he cradles Gyro's face and asks for forgiveness. (it's a major moment. to me)

Chapter 44: A Silent Way (Part 5)

5) Ok this one is just a little sus but I'm putting it in anyway: Gyro dreaming of that time he slept with one of his patients, only to immediately wake up and have a domestic scene with Johnny. For what purpose...?

Chapter 45: The Promised Land Sugar Mountain (Part 1)

6) Johnny gives up the corpse parts for Gyro (again), immediately followed by them drinking away their sorrows into the sunset. Who's doing it like them.

Chapter 48: Tubular Bells (Part 1)

7) Gyro finds the Golden Rectangle, previously described as, “… the foundation for every perfect structure for beauty" (Chapter 43: A Silent Way, Part 4) in Johnny eyes, and refuses to answer Johnny's question about where he's finding it. The implications of what Gyro thinks of Johnny's physical appearance are obvious.

Chapter 52: Wrecking Ball (Part 2)

8) Gyro sacrifices his hand, his only other point of reference for the Golden Rectangle, in order to save Johnny from a hit he probably could have tanked. Even Gyro looks a little surprised at himself... Also, they are all over each other this arc. Gyro is especially protective.

And, a little later:

Chapter 53: Wrecking Ball (Part 3)

9) Once it's revealed that Valentine intends to kill the rest of the racers (at least the ones who pose a threat to him), and makes an attempt on Johnny's life, Gyro attempts to convince Johnny to drop out, implying that he would drop out with him.

Of course, this is immediately followed by Johnny begging Gyro to, at the very least, help Lucy and see what she knows about the corpse parts. Seeing Johnny's distress at being so close to his goal only to have it snatched away from him convinces Gyro to stay in the race (something that will ultimately get him killed) and theorize how they can use the spin to defeat Valentine (via the stirrups). He tries to play it off but goddamn he is in love with him.

Chapter 72: Ticket to Ride (Part 2)

10) Shuiesha coloring may imply that Johnny is wearing Gyro's shirt beneath his own?? It's got the same collar and everything.

First appearance of this coloring choice is Chapter 63: 7 Days in a Week

11) Exchange of secrets no one else knows (they are each other's most important person!)

This panel in particular:

Chapter 76: D4C (Part 9)

12) And last but not least, thee set of chapter titles ever, in which Valetine attempts to bargain with Johnny to spare his life in return for bringing back Gyro. Johnny refuses, not because of any moral quandary about saving the life of an evil man, but because the Gyro brought back would not be the same. On top of that, he recognizes Valentine as a liar.