Perhaps the old friend has changed a great deal since they last saw Reid. They could be in trouble and turn to Reid for help. As Reid tries to assist them, he discovers secrets from their past that they had both forgotten or repressed, which adds depth to their relationship.
One idea could be that the old friend resurfaces after many years and is somehow involved in a case Reid is working on. Maybe they have some hidden knowledge about the unsub that helps Reid solve the case while also reigniting their friendship.
One interesting plot idea could be that Tony and Spencer are assigned a particularly difficult case. They have different approaches at first, with Tony relying on his street smarts and Spencer on his vast knowledge. As they work together, they start to understand and respect each other's methods more, and in the end, they solve the case in a way that combines both of their strengths.
Perhaps in the fanfic, the OC has a special skill that Reid needs to utilize. However, due to some misunderstandings, he has to handcuff her first. This could lead to a story of them overcoming their differences and working together while the handcuffs become a symbol of their initial conflict and later connection. For example, she might be able to read ancient languages and Reid needs her help with a case involving historical documents.
One plot idea could be that they discover they are brothers through a mysterious family secret. Maybe there's a hidden inheritance or a long - lost relative that leads them to this realization. Another could be that they have to work together to solve a crime that has a personal connection to their new - found brotherhood, with their different skills complementing each other. For example, Tony's street smarts and Reid's academic knowledge.
A more comical plot could be that they are forced to live together for some reason, like a family obligation. Tony's more outgoing and Reid's more introverted nature could create a lot of humorous situations as they try to co - exist. For example, Tony might try to get Reid to go out and party, while Reid just wants to read his books in peace.
The relationship can be developed by having them rely on each other. If the old friend has a problem, Reid uses his intelligence and skills to help. In return, the old friend can offer Reid emotional support, which he often lacks in his high - stress job. This mutual support system can realistically build their relationship over time.
One idea could be focusing on Spencer's over - protective nature. Since he's highly intelligent, he might research every little thing about pregnancy and drive his wife crazy with all his facts and precautions. For example, he could be constantly worried about her diet and make sure she's getting all the right nutrients.
A plot could involve the OC using their lip - reading to communicate secretly with Reid in a dangerous situation. Like when they are held hostage by a group, and the OC lip - reads the plans of the captors to Reid without the captors noticing. Then there could be a romantic sub - plot where Reid is initially intrigued by this unique skill of the OC and gradually falls for their personality as well. The OC might also be in danger because of their lip - reading ability as someone wants to keep their secrets hidden.
Well, a great non - sexual fanfiction concept involving Spencer Reid could be set in an alternate universe where he's a college professor instead of an FBI agent. He could be teaching a class full of diverse students, and the story could revolve around his efforts to inspire them and help them overcome their academic and personal challenges. Or perhaps a fanfiction where he travels back in time and meets some of the great minds in history, like Einstein, and they have intellectual discussions. Also, a story about him starting a book club within the BAU could be interesting, focusing on how books bring the team closer together.
In one fanfiction, Reid meets a girl who is an artist. She's doing a project on the human mind and how it can be expressed through art. She approaches Reid to learn more about the criminal mind for her art. As they work together, Reid is fascinated by her unique perspective. They start to develop feelings for each other. Their relationship grows as she tries to show Reid the beauty of art, and he tries to show her the complexity of the human mind.
A great Spencer Reid meets BAU fanfiction could be centered around a time - travel plot. Reid somehow gets sent back in time to when the BAU was first formed. He has to use his modern - day knowledge and skills to solve cases in the past while also dealing with the different personalities and procedures of that era. Another type could be a love - story - based fanfiction, where Reid falls in love with a new agent in the BAU. Their relationship develops as they work together on various cases, facing challenges both in their personal lives and in the high - stakes world of criminal profiling.