Sorry, but this dropped off my radar
OK, I've got your name: Aikido Hiei-kai （合気道秘影会）
"Hi" secret or hidden
"Ei" (also "kage") is shadow or silhouette
I like this kage rather than 蔭 because it carries more a connotation of the shadow of a form (as of a person, etc) rather than simply the darkness itself which is caused by a blockage of light. Also "hiei-kai" is more euphonious than "hiin-kai" (could be mistaken for "the aikido committee" - although come to think of it that's kind of a cool name too
If you're unsure of the pronunciation, just say "he ate kai", but without the 't'