I just have to say the Seijoh extra hits completely different now that we know Oikawa left Japan altogether and went to Argentina. That thank you isn’t just a thank you for their time together in volleyball, but he’s also saying goodbye since they’re not even going to see each other anymore.
He’s sobbing because this is really it and all of the promises they made to go to nationals together die there. They believed in him, and he couldn’t take them to the final goal. And now it’s over and he has to leave to go abroad alone. They all tried so hard and it just wasn’t enough.
“When you run with the Doctor, it feels like it will never end… but however hard you try, you can’t run forever. Everybody knows that everybody dies, and nobody knows it like the Doctor. But I do think that all the skies of all the worlds might just turn dark if he ever, for one moment, accepts it…”