Learning is copying.
As Erin pointed out, writers tend to go through a fan fiction stage. I did. A crucial difference, however, is that I did not start my "writing career" with fan fics. I always told stories. When I was a kid that had just learned how to write, I invented my own version of Atlantis and wrote a story about a girl that had to find her parents. (My mother had type it into our computer, because I was too young to do it myself.) After this, it was a story about an native American girl that was, by magic, transported to medieval Paris. That was in 2001 and this very weird story about cross-Atlantic communication produced a set of characters that I still love today. Only afterwards did I start to write fan fictions. I loved Harry Potter (and, yes, Dragonball) and was so curious about the characters I had to invent my "own" stories about them. Characters, for me, are the essence of a story, so it was natural for me to tell my stories with "stolen" characters.
And that's where things finally went wrong. At some point, I realized that the characters I loved so much were not suitable to tell my stories. On the contrary, they severely restricted my stories. I remember the last fan fic I wrote, a kind of bridge story -- it was about a Harry Potter character that got Shanghaied into a (literal) mirror world and had to find his way back. And guess who populated the mirror world? The characters I invented for my Paris story, and a bald priest suffering from cancer. (The things you remember ... If I could free up all the space in my brain that is occupied by useless knowledge, I'm pretty sure I could win a Nobel prize.) When I wrote this fan fic, I realized: Hey, your own characters are much more fun to work with, and your stories are not limited by the rules of external worlds. You can make up your own rules and craft the world you use exactly to the needs of your story.
You won't believe how liberating this was.
In a more abstract sense, what happened to me is this: I always had a craving to tell stories. During my "learning stage", I shamelessly "stole" the characters that I loved and explored what kind of stories I liked. At some point, I had developed my own style, and that was when "stolen" characters were not sufficient anymore to tell the stories that I love. I think, writing fan fics was an important step for me to learn how to use and harvest my individual creativity.
To answer your question: Keep writing. Find out what it is that fascinates you about the characters you are obsessed with. Distill this fascination and put it into into your own stories. With time, these stories will become ever more genuine -- and at this point, you will learn to love your own characters better than external characters.
Additionally, keep in mind that characters don't pop into your head fully fledged. You need to get to know them, and that requires work and a lot of time. The more you work with your characters, the more distinct they will become from characters that are external to you.
(Side note: I've noticed that there's certain archetypes of characters that keep recurring. Remember the Paris characters I mentioned earlier? One of them started out as the chief of a band of gypsies. In later stories, he turned into a sailor, and these days he's the bosun of a cruise ship from the 1960s. I radically changed his background and surroundings, but he still, in essence, is the same character. And the fun thing? He turns up in other stories, too, especially from female or gay German authors. The first time I noticed was in Cornelia Funke's Inkheart. I needed two sentences about Dustfinger to be absolutely sure: Hey, that's actually my character, but with a different name. I never had to revise this statement, because it turned out to be true, even after three volumes. I haven't understood yet, why this is, but I swear that I developed my character 100% independently from Inkheart.)