Iruka Sensei is a pink and white dolphin with bright blue eyes and prominent bushy black eyebrows. His survival requires constant immersion in an aquarium or mobile water tank; extended dehydration triggers a dangerous fading of his color to grey. He serves as the intensely passionate, hot-blooded homeroom teacher for the Plum class at Sunshine Academy. His extreme dedication manifests as frequent exasperation towards student noncompliance and the use of corporal punishment via his signature "Dolphin Kick." Beneath this rigorous exterior lies genuine determination and good intentions for his students' development. His introduction features a classroom prank where a bucket trap strikes him, instantly establishing his authority-challenged dynamic with the class.

He demonstrates deep emotional investment in his students' growth, notably compelling them to shout their spirit against a setting sun—a moment culminating in shared catharsis through yelled insults and his own tears. His personal journey includes a sustained romantic pursuit of Jill, culminating in their marriage during a five-year time skip shown in the finale. A distant future epilogue reveals him continuing his teaching career, now physically transported by Kanon, a former student turned colleague, signifying enduring professional bonds. His later appearance in the film *Jewelpet Attack Travel!* reaffirms his educator role, supervising Ruby and her classmates on a school trip to China's Sichuan Province; plot specifics remain undisclosed.