The OC shop owner could be a former member of a secret society that has knowledge about the Justice League's enemies. They use their shop as a cover while secretly helping the League by providing intel. For example, they overhear conversations from villains who visit the shop thinking it's just an ordinary place.
The OC shop owner might be a magic user. Their shop could be filled with magical items. When the Justice League faces a magical threat, they turn to this shop owner for help. The shop owner could then join the League on their mission, using their magic items and skills to defeat the enemy.
One idea could be an OC vampire who joins the Justice League under false pretenses. Maybe they claim to want to use their powers for good, but in reality, they have a hidden agenda related to their vampiric nature, like finding a powerful magical artifact within the Justice League's HQ.
One idea could be that the female vampire OC is initially a foe. She might be causing chaos in the city, perhaps by preying on criminals at first but then getting out of control. The Justice League has to figure out how to stop her without killing her. They discover she has a tragic backstory that led her to become a vampire, and they try to rehabilitate her.
One idea could be an OC God who has the power to manipulate time. This God could be a new threat to the Justice League as they struggle to understand and combat this power. For example, the God could reverse important events in the League's history, causing chaos.
One idea could be an OC with the power to manipulate time joining the Justice League. They could accidentally create alternate timelines while trying to stop a villain, and the Justice League has to fix it. For example, the OC might go back in time to prevent a major disaster but end up changing the course of events in a way that makes the villain even more powerful in the new timeline.
One idea could be an Immortal OC who has ancient knowledge and uses it to help the Justice League prevent a threat that was foretold in a long - lost prophecy. For example, this OC might know of a hidden weakness in an upcoming powerful villain.
Maybe the OC Kryptonian has a power that is malfunctioning. They struggle to control it and it causes problems within the Justice League at first. But through the help of other members like Superman, they learn to master it. This could lead to a story of self - discovery and friendship within the team. They could face a villain who specifically targets their power, making it a race against time to get it under control.
One idea could be an OC who is a long - lost relative of Aquaman. They could have unique powers related to water control but in a different way than Aquaman. For example, the OC can turn water into different shapes and use them as weapons. Another plot could involve the OC being from a hidden underwater tribe that has a different view on Atlantis's rule. The OC could try to bridge the gap between their tribe and Atlantis while also joining the Justice League to fight common threats.
One idea could be an oc who is an old god's descendant and tries to join the Justice League. They might have unique powers that both amaze and worry the League members.
One idea could be that the OC has a unique power that the Justice League initially distrusts but later comes to rely on. For example, the OC can manipulate time in small bursts, which at first seems dangerous but is actually crucial in stopping a villain who can freeze time.