Basically, just as the title says.

The first question is, from a storyline perspective, who actually broke the cycle of death and Sin in Spira? Was it Tidus? Yuna? Auron? Rikku? A combination of some characters? Give me your thoughts on the matter.

The second question is, was Tidus even a necessary part of the storyline? Everyone that hates Tidus' guts all complained that he wasn't at some point, but most never explain their reasoning. I want to see us come to a sort of general consensus as to whether or not he needs to be in the game, and during what parts he really isn't necessary at all.

I'll post my thoughts after a few people reply.