A possible start could be that Lucifer is lured into a trap by a powerful being. Once in the trap, his powers are removed. A group of characters who have been wronged by Lucifer in the past then enter the scene. They discuss what to do with him, and one of them suggests the rather unorthodox spanking as a way to start making him pay for all the harm he has caused. This could set the stage for a story full of conflict and power struggles.
It could start with Lucifer waking up in a strange place, realizing his powers are gone. Then, he's immediately confronted by a character who has long hated him. This character decides to take advantage of his powerless state and starts the spanking as a form of revenge. For example, it could be a demon who was once under Lucifer's thumb but now has the upper hand.
The fanfiction might begin with a big battle where Lucifer's powers are somehow nullified. As he lies there, defeated, another character approaches. This character has a personal vendetta against Lucifer. They start by taunting him about his now - powerless state and then, in a fit of anger and a desire to assert dominance, they spank him. This could be a human who has been affected by Lucifer's actions throughout their life.
In this type of fanfiction, a powerless Lucifer might start to experience emotions in a more raw and human way. Without his powers, he's no longer the all - powerful being. He could become a target for his former enemies who see this as an opportunity for revenge. This could lead to a series of adventures where he has to rely on his wits rather than his strength. He might also start to question his own identity and purpose, which were so closely tied to his power before.
One idea could be that Lucifer has his powers stripped by a powerful spell cast by a group of witches. As a result, he's in a vulnerable state and some other characters, perhaps angels who have a bone to pick with him, decide to teach him a lesson in a rather unorthodox way like spanking. It could be a humorous take on the usually intimidating Lucifer.
A powerless Lucifer could survive among humans by using his charm and intelligence. He's been around for a long time and has a lot of knowledge. He could use that to blend in and perhaps find some humans who are willing to protect him out of pity or curiosity.
Another plot could be that he is captured by a group of hunters who plan to keep him powerless. They try to use him as a bargaining chip with other demons or angels. But Lucifer, being clever even without his powers, tries to turn the situation around and manipulate the hunters to his advantage.
If in a Supernatural fanfiction Lucifer becomes powerless among humans, first of all, his entire view of the world would change. He has always been at the top of the power hierarchy, looking down on humans. But now, he's in their shoes. He'd likely be in a state of shock initially. Then, he might try to find a way to regain his power. But in the process, he could form unexpected alliances with humans. Some might see him as a fallen being in need of help, while others would be out to take advantage of his weakened state.
One interesting fanfiction could be 'Lucifer's Trial by Blade'. In this story, Lucifer gets stabbed during a battle in the underworld. The author vividly describes his pain and the chaos that ensues. It's a great read if you like action - packed fanfics.
One possible plot twist could be that the pregnancy is not as straightforward as it seems. Maybe there are some supernatural elements involved, like the baby having special powers. For example, the baby could be a key to a different realm or have the ability to manipulate time. Another plot twist could be that there are enemies who want to harm Chloe because of the pregnancy, adding a lot of action and suspense to the fanfic.
One consequence could be that he becomes more aware of privacy boundaries. For example, if a boy is spanked for peeping, he'll likely think twice before doing it again to avoid the pain.
One story could be that two friends, Tom and Jerry (not the cartoon characters), were playing a prank at school. They put glue on the teacher's chair. As a result, the teacher decided to spank them both as punishment in the old - fashioned way. They learned their lesson not to play such mean pranks again.
One story could be that a child confessed to his mom about breaking her favorite vase while playing ball in the house. His mom was so angry that she spanked him. But later, she also hugged him and told him it was important to be honest.