Eusine, known as Eugene in the English dub of "The Legend of Thunder," is a researcher dedicated to studying the Legendary Beast trio, with a singular focus on Suicune. His pursuit of Suicune, sparked by childhood tales from his grandfather, has driven him for over a decade and remains his core motivation.

He possesses a competitive drive and determined nature, readily accepting battles to prove his skill as a trainer. Initially skeptical of others' claims about encountering Legendary Pokémon, he isn't afraid to challenge such assertions. Yet, he adapts his views, showing respect for trainers whose genuine dedication earns a Legendary Pokémon's trust.

In "The Legend of Thunder," he aids in protecting Raikou from Team Rocket operatives Attila and Hun. After Raikou flees an injured escape from a Pokémon Center, Eusine mobilizes Jimmy and Marina in his vehicle to pursue it. During the clash with Team Rocket, he contributes strategically. His Alakazam supports the coordinated attack by Jimmy, Marina, and Vincent, disrupting the Miracle Crystal's energy field to free Raikou. Witnessing the trainers' selfless defense of their Pokémon and Raikou prompts a shift in his perspective on human-Pokémon bonds. He acknowledges Raikou's ability to identify trustworthy humans and expresses respect for Jimmy's connection with the Legendary Pokémon following the rescue.

His known Pokémon is an Alakazam, deployed during the final confrontation to bolster the other trainers' Pokémon assaulting the Miracle Crystal.