Kenji Oyamada provides comic relief within his elementary school class at Umi no Hoshi, alongside classmates Sasami Kawai and Misao Amano. Recognizable by his squinty eyes and slight build, Kenji shares a close bond with Hiroto Majima, frequently seen together playing soccer after school or spreading rumors about Pretty Sammy sightings.

Despite academic prowess, demonstrated by scoring a perfect 100 on a test alongside Misao, Kenji initially struggles physically, notably failing to clear a vaulting box and landing on top during gym class. He later practices diligently with Hiroto to improve. Kenji actively participates in sports, enjoys soccer, and possesses knowledge of unconventional dodgeball techniques learned from a book.

His prominent hobby is photography; he routinely carries his camera. During a school trip to Washu's research island, he photographed Mihoshi in her swimsuit, complimented Kiyone's beauty, persuaded Pixy Misa to pose, and captured Eimi Date in her magical girl form.

Kenji's comedic role surfaces through his eccentric actions: suggesting the Bon Odori funeral ritual for the school festival, remaining unaffected during a massive heatwave, putting rocks inside snowballs meant for the Lovely Madams, and being swept away by a wave of cheese all the way to Papua New Guinea. These moments consistently inject levity into events.