He is voiced by Tasuku Hatanaka in the Japanese version of the anime, and by Kyle Phillips in the English version of the anime.
Denki has blond hair with a black lightning-shaped streak and small, thin eyebrows.
Denki's first Hero Costume consists of a black jacket that he wears open with lightning patterns, a white shirt underneath, a belt, black pants with one stripe running down each leg, and a headset.
Denki's second Hero Costume consists of a shorter black jacket with fewer lightning patterns, a white shirt, a belt, black pants with one small white stripe running down each leg starting from his knees, a choker, a smaller black headset, blue optical lenses, and a Pointers' shooter on his right arm.
Denki is a friendly, social and energetic boy. While he is rather casual when interacting with others, including even antagonistic people like Katsuki Bakugo, Denki also becomes quickly distraught when he is put into stressful situations. He may come off as blunt and reckless sometimes, but is always well-meaning.
Denki is somewhat flirtatious towards the girls of his class (and even the ones from other classes), trying to pass himself off as a smooth talker. He is not very lucky with his approaches though, frequently getting ignored or outright rejected by everyone. Although, he does seem to have a steady friendship with Mina Ashido and, occasionally, Kyoka Jiro. He is also slightly mischievous, joining in pranks occasionally. Overall, it appears that Denki has an interest in looking cool in front of others, but has a shallow understanding of how to do so. As such, he gets easily influenced by what's popular at the moment.
Denki is not very academically bright, requiring help when it comes to studying. He does not appear to show much interest in classes and tests tend to make him anxious. Despite this, he can show surprising knowledge about certain areas such as literature, art and music, possessing a large vocabulary. His overall lack of wit often makes him a common victim of snark, in particular from Kyoka.
During combat situations, Denki is very quick to panic, which leads him to activate his Quirk in anticipation. He also becomes more reluctant to use his full power when there are allies close to him, being afraid of hurting them through collateral damage. When he is assured that all his allies will be safe from his powers, he becomes more confident in his fighting abilities. He does not tolerate others looking down on him or his classmates and will defend them if necessary.
When Denki exceeds his wattage limit, he loses his ability to use his Quirk and his entire personality becomes that of a giggling idiot until he turns back to normal. In this form, he is always giving thumbs-ups, as a way to let others know that he is fine.