ZIX is a two-man idol unit from the previous talent company Koki, Kensuke and Ryota belonged to, and I assume these two were the two talents
said company chose to debut, instead of Koki, Kensuke, and Ryota (ALIVE Sono 1 Side.G).
Sugai Makoto (voiced by Hamano Daiki) ZIX’s leader. A relative of the president of a certain entertainment company, he is a young man whose arrogance is as strong as his talents. He is the type of person who has many rivals, yet possesses a wildly enthusiastic fanbase. Has always seen Koki as a rival, and is highly conscious of it. (source)
Hishida Mitsuru (voiced by Watanabe Takumi) The other half of ZIX. Known among fans as someone who gets into the mood very quickly, but is actually a rather calculating, ambitious person. Has a rather troublesome personality, where he tends to torment or bully anything he likes or is fond of; there are also instances where he provokes Makoto. Ryota’s natural enemy. (source)