Rinsagi

Rinsagi is the slash ship between Itoshi Rin and Isagi Yoichi from the Blue Lock fandom.

Canon
The first time Isagi sees Rin is in Chapter 40 when the Second Selection began. Rin didn't falter like the rest of them and immediately went through the gate after kicking two balls and making them collide with each other in midair, showcasing his skill. Isagi describes Rin's kicks as beautiful and clean, calling him incredible.

After Rin goes through the gate to the Second Selection, the screen above it displays the words "Challenger: Itoshi Rin". Team Z draw parallels to the genius Itoshi Sae from the New Generation's World 11.

After forming a team of three with Bachira and Nagi, Isagi enters the Third Stage with them to find Rin, Aryu, and Tokimitsu waiting for another team to arrive. Isagi recognises Rin immediately and is at first hesitant to battle him, but after learning that not only does the winning team get to steal one of the losing team's members, but Rin is indeed the younger brother of Itoshi Sae, his "ego" urges him to fight Rin.

Isagi is determined to win and steal Rin, but Rin's immense talent overwhelms everyone on the field, even his own teammates. Rin scores a goal with a straight shot from the centre line in the kick off, calling them all lukewarm and a waste of time. This is where their rivalry really begins to stem. Isagi calls Rin lukewarm (aka Rin's catchphrase) for not thinking he'd be able to see the same scenery. In the final moments of the game where the score is 4-2 in Rin's team's favour, Isagi believes can control the field and take back the game, but for the first time Rin approaches and challenges him. Isagi thinks Rin's underestimating him, but Rin, who Isagi then realises is who's really in control, sees right through his plans.