What is a former production company that the animator of the Level C video animation worked for?
Level C:  It has also been made into an original video animation by J.C.Staff. J.C.Staff: J.C.Staff Co., Ltd. (株式会社ジェー・シー・スタッフ , Kabushiki gaisha Jē Shī Sutaffu , J and C stand for "Japan Creative") , is a Japanese anime studio founded in January 1986 by Tomoyuki Miyata, who previously worked at Tatsunoko Production.
Tatsunoko Production