To summon demons, he "plays" a guitar-like COMP. He attempts to deal with Spooky who had infiltrated Algon Soft NS. He summons the demons found in the building and runs into the protagonist after the Spookies come to rescue Spooky. Carol attempts to kill the protagonist for being a summoner not part of the Phantom Society and summons a Padlock, Ippon-Datara, and two Pretas to fight him with. After losing he retreats, accidentally dropping his license card and an encrypted code containing the web address to Summoner Net.
During his second encounter with the protagonist he attempts to summon the Great Angel Kokabel to get revenge on the Protagonist for beating him and making him a laughing stock to even Finnegan, but instead summons the spirit Moowis. Moowis proceeds to absorb his body and spits it out, with Carol's body now partially transformed and possessed by Moowis. After Moowis' defeat he leaves behind Carol J's still living body, who decides to leave the Phantom Society. He also gives the protagonist the "Back Upper" COMP software, which allows him to save anywhere.
In the PlayStation and 3DS version, after he quits as a summoner he appears in Yurashima after Satanael's defeat as a street musician. He also appears as an opponent in the Casino Blizzardon's VS Poker under the name "Gambler J."