Harlockeanism

In Harlockeanism, there is only one belief and creed which also spells out it's Oath, the rest being up to the individual Harlockean:

In his own words, he "fights for no one's sake, only for something deep in his heart." Likewise, he shows no fear of death.

So the personal Oath to take is: " I fight for no one's sake, only for something deep in my heart."

Harlockeanism is a real religion based on the fictional Space Pirate, Captain Harlock, who inspired the movement. But the focus is on fighting for what you believe in and not on Captain Harlock, though admired and highly revered by Harlockeans.