In episode 5 of Oregairu S2, Hachiman enlists Zaimokuza's aid in getting Iroha elected president. Zaimokuza then goes on to give Hachiman an earful about how he doesn't want to be the fall guy for the scheme and how Hachiman had better take responsibility, and all of that.
But what role did Zaimokuza even have in the scheme? It looked to me like Hachiman did all the work in setting up the Twitter accounts and pulling the bait-and-switch.
I don't really remember how the anime showed it, but in the light novel Hachiman and Zaimokuza both split up the Twitter accounts between them. Then the night before the day that Hachiman shows the printouts to Irohasu, he had actually called Zaimokuza to change the accounts' display name and images to "Isshiki Iroha Grassroots Account". Understandably Zaimokuza was not very enthusiastic about it, and only agreed after he was convinced that he wouldn't be blamed for it.
That phone call is right in the beginning of chapter 8 of volume 8. So yeah the 'switch' part wasn't done by Hachiman himself. He did take the printouts later though.
