Shinkai attended a municipal elementary school in Maebashi in his youth. He enjoyed playing soccer, and also music. He played the saxophone and joined a brass band. Shinkai won the gold medal at the Gunma Prefectural Brass Band Competition in the summer of the second and third years of junior high school. Shinkai decided to become a manga artist after failing to find a job in the music industry. After graduating from university, Shinkai was employed as Hirohiko Araki's assistant for about 5 years.
After being independent, Shinkai published four one-shots from 2004 to 2009. His debut work was "ensemble" published in the 2004 Summer "Jump Next!" issue, a work themed around a brass band. He followed it with "Heart Catcher" published in the 2005 Summer "Jump Next!", then "Dodge The Ball" in the ninth 2007 issue of Weekly Shonen Jump with dodgeball as a theme and "Q part !! in the thirtennth 2008 issue of WSJ.
His first serialized work was LIGHT WING, a soccer manga published in WSJ from 2010 to 2011. He followed it with another series called SOUL CATCHER(S), a manga about music published from 2013 to 2016. His next serialized work was "Instant detective Shun Hirameki", a manga adaptation of the variety/quiz show "Tonight Nazotore".
- ensemble (アンサンブル) (One-shot, 2004)
- Heart Catcher (One-shot, 2005)
- Dodge The Ball (One-shot, 2007)
- Q part !! (Q部!!) (One-shot, 2008)
- LIGHT WING (Series, 2010-2011)
- SOUL CATCHER(S) (Pilot one-shot, 2012)
- SOUL CATCHER(S) (Series, 2013-2016)
- Day and night reversal circle Strongest (昼夜逆転丸) (One-shot, 2017), spin-off of Soul Catcher
- Buzzle Juggle (バズルジャグル) (One-shot, 2017)
- Instant detective Shun Hirameki (瞬間探偵 平目木駿) (Pilot one-shot, 2017)
- Instant detective Shun Hirameki (瞬間探偵 平目木駿) (Series, 2018-2019)
- Like for the first time (はじめてのいいね) (One-shot split in two chapter, 2019)