Has an anime been done about a key?

i mean like a character holds a key that just about everyone wants that holds secrets to just about everything. the character would be very skilled in battle or have someone with him or her that is very powerful. the key could be like to a door or a treasure chest that would grant anybody anything they would desire. the reason i want to know is because i am interested in writing a full series on it and this because my favorite pass time is to write i have written a lot of anime stories but they have been lost or erased through the years now im left with like 5 or 8 stories im not sure. thanks