Summoning.

You have a talent for the magic art of summoning, one of the more intricate and hard to learn forms of magic but somehow it is the only form of magic you are capable of apart from the aforementioned casanova effect.

The art of summoning is more diverse and more powerful then most people believe, even a lot of mages underestimate it and you intend to prove them wrong.

You parents subtly started to test which forms of magic you had a talent for as soon as you started to walk but tried to incorporate it in games so as not to punish you with it or push you in a certain direction. When they discovered your singular talent you were encouraged to use it in many ways and so your earliest friends were summoned beings. Your most powerful summon, the only one you have an actual contract with, is one you summoned and befriended at the age of five. She's a centuries old fire dragon who usually appears in a humanoid form and calls herself Tear. It's easy to forget how old and experienced she is as Tear acts and speaks as if she is in her early twenties. Maybe she is that old compared to a dragon's long lifespan but you doubt it. Her way of speaking fits well with her bubbly, submissive yet proud personality. Scratch that submissive part as she's only submissive to you and only because she recognizes you as a worthy master in both skills and personality.

To illustrate the versatility of the art of summoning, you can infuse your summoned creatures with certain spells to upgrade their attributes and/or grant them extra abilities. You can also summon equipment for your familiars and yourself and you can summon totems that deal damage to enemies within their range using an element based on the area they are summoned in. Another thing you can do is to summon an ability of your familiar without actually summoning her so Tear's dragon-breath can be summoned without summoning the dragoness herself. There are of course even more ways to use the art of summoning but even most of these ways to use the art are forgotten.

When you receive an invite to be mentored by a hero of the JLA you guess that someone there has gotten wind of your abilities and doesn't want a fire dragon to end up aiding villains. She may enjoy battle but Tear would not have recognized you as her master if you were going to be a villain so their worry is unfounded. You decide to take the opportunity to learn from an experienced hero, knowing that the Casanova effect will likely ensure that said mentor will be a beautiful woman.

The question now is: How do you go to the watchtower and how do they react to your arrival?