Akira Yamaguchi, one of the smartest students in Nube's class, is also the one that goes through a slight character change as the series goes on. At the start of the series, Akira is merely a bright, but slightly unlucky boy who tries his best but can never achieve what he's capable of. The source of this bad luck was a near-death experience where he went to the Sanzu River, where a youkai consistently stops anyone that tries to complete their tasks. After Nube exorcises this spirit, Akira finds a bit more luck, but remains a more generic character. But later in the series, Akira's modest personality changes towards that of being the "mad scientist" of the class, consistently using technology to bridge the gap between humans and youkai and showing off in order to do so. Originally, Akira was paired alongside Hiroshi, Kyoko, Makoto, and Miki as part of the main set of students whom allies with Nube. But because of Akira's earlier "plain" personality, he fell out of favor over more dynamic characters like Katsuya. Regardless, he does remain a semi-major character throughout the whole manga run. Like Miki, Akira's name is based on the main male lead in Go Nagai's Devilman.

(Source: Wikipedia)