|This article is about a/an suit/voice actor in the Super Sentai series.|
His roles in Super Sentai tend to be connected to Sentai Reds. He was the substitute suit actor for Gosei Red in Tensou Sentai Goseiger. In Kaizoku Sentai Gokaiger, he was the suit actor for Basco ta Jolokia's monster form, Basco being the nemesis of Gokai Red. He also played Gavan in-costume in Kaizoku Sentai Gokaiger vs. Uchuu Keiji Gavan: The Movie, where it is shown that Gavan gave Captain Marvelous the courage that would make him a hero when he grew up. Then in Tokumei Sentai Go-Busters he was the suit actor for Cheeda Nick, the BuddyRoid and older brother figure to Red Buster, as well as his mecha, Go-Buster Ace. He was the suit actor for Zyuoh Eagle in Doubutsu Sentai Zyuohger.
On the day of the last filming of Ressha Sentai ToQger, Kosuke broke his thumb in one of his practice. The injury caused him to be decommissioned for two months, with the role as AkaNinger was temporarily given to Yugo Fujii. Eventually, he recovered from his sickness and returned to work, first as HurricaneRed's suit actor and later return as AkaNinger once more. 
After Zyuohger, his role as a Sentai Red suit actor is taken over by Masashi Takada during Uchu Sentai Kyuranger, while he was serving as a suit actor for Kamen Rider Cronus in Kamen Rider Ex-Aid. He returns as a Sentai Red suit actor for Lupin Red.
- Tensou Sentai Goseiger - Gosei Red (sub)
- Kaizoku Sentai Gokaiger - Action Commander Regaeru (voice; episode 27), Basco ta Jolokia (true form)
- Tokumei Sentai Go-Busters - Cheeda Nick, Go-Buster Ace, Gavan Type G (Kōsuke Asai was also the suit actor for Gavan Type G in Uchuu Keiji Gavan: The Movie)
- Zyuden Sentai Kyoryuger (2013-2014) - Kyoryu Green
- Ressha Sentai ToQger (2014-2015) - ToQ 6Gou
- Shuriken Sentai Ninninger - Yokai Kasha (episode 6), HurricaneRed (episode 7), AkaNinger (episode 8-47 present)
- Doubutsu Sentai Zyuohger (2016-2017)- Zyuoh Eagle
- Kaitou Sentai Lupinranger VS Keisatsu Sentai Patranger (2018-2019) - LupinRed