He first appeared in Pop Goes The Sneasel where he met Ash and his friends at the summit of the Ho-Oh shrine. He overheard the shrine guard ask Ash if he would help ward off what was preventing them from getting Ho-Oh's sacred flame. Immediately Harrison offered to help too. Later hearing that it was a Sneasel that was attacking those who approached the sacred flame, he had started to make plans on catching it. Once at the top of the stairs, Harrison instructed Ash to try to get the flame while he and Misty distracted Machop and Machoke. However he underestimated Sneasel's strength and he was forced to come up with another plan.
Using Houndoom and Phanpy, Harrison and Ash took on Machop and Machoke together; their goal being to take them both out before they would get to Sneasel. Both of their Pokémon were able to hurl Machop and Machoke down the stairs leaving Sneasel by itself. After Team Rocket's brief interruption, Harrison used his Blaziken to take down Sneasel and he was able to capture it. At the end of the day, Harrison told Ash that he would meet up with him again at the Silver Conference.
After many cameos during the qualifying rounds of the Silver Conference and wishing Ash luck in his battle with Gary in The Ties That Bind, Harrison appeared in Can't Beat the Heat!, where he and Ash began their six-on-six battle. It continued in Playing with Fire! and Johto Photo Finish. In the latter episode, Harrison defeated Ash, but went on to lose to Jon Dickson.
It was Harrison who convinced Ash to go to the Hoenn region. He told Ash about Professor Birch and all the Pokémon that Ash had probably never seen before.
Following the Silver Conference, Harrison went to Kanto to participate in the Indigo League.