Sei began his acting training in high school and has a BFA in acting from New York University (Tisch School of the Arts). While training at Stella Adler Studio, he worked for Pan Asian Repertory as an actor and director for a few years.
Sei left New York in 1996 in search of diverse acting methods/techniques in the world. He travelled across Europe where he worked with artists from Russia, Bulgaria, Norway, Italy, England and Japan (including Yoshi Oida).
Sei arrived in Paris in 1998 and became artistic director at Bilingual Acting Workshop. He then founded his own acting studio (KEYS Acting Studio) in 2012 and is currently in charge of the acting program at Studio Artifex.
As a private coach, his clients have appeared in such films as Dunkirk, Mission Impossible 6 – Fallout and also in various TV shows on Netflix, Amazon Prime, Canal+, TF1, France 2 and 3.