u/AAAANNNNAN

Rin always believes that Isagi is the "no.1" material with him.

When Hugo said "Isagi you are not no 1",

Rin comforted Isagi and tell him he is a "no 1".

When the whole team plays around Karasu, Rin never joined in the system or stated that Isagi should work as "no 2"

But when Isagi "abandoned" the no.1 path, this is where Rin got pissed off. Rin thinks Isagi is "no.1" not some hybrid no1 no2 thing Isagi just invented. I believe that's what make Rin crashes out, he feels like Isagi giving up before Rin himself.

(I'm not saying Isagi is wrong Rin is right, but in Rin's eyes only correct answer is to be no1 and Isagi gave up)