One common theme might be growth. The 'spirit' and 'rain baby' characters could go through personal growth, learning about themselves and the world around them.
Another theme is transformation. The rain can symbolize change, and the spirit may go through a transformation, either physically or emotionally. In some stories, the spirit might gain new powers or a new understanding of itself after being exposed to the rain for a long time. This theme adds depth to the stories.
Another theme is the challenges they face as a couple. This could be external factors like family or society not fully accepting their relationship, or internal struggles within themselves. For example, in some fanfictions, one of them might be afraid of commitment at first.
Adventure is also common. They could be on a quest to find a lost item or to explore a new part of their world. It makes for exciting reading as they face various challenges as babies. For instance, they might encounter a small stream that they need to cross but are too small to do so easily. And they have to figure out a solution together. This kind of adventure - based theme is quite popular.
The contrast between dark and light, both literally and metaphorically, is a significant theme. The 'rain' might represent the difficult, sad, or negative aspects of life, while the 'sunshine' represents the positive, happy, and warm elements. This contrast is used to create interesting storylines and character developments. For instance, a character might be in a state of despair (the rain) but then is shown a way out by someone positive (the sunshine), leading to a journey of self - improvement and new - found happiness.
One common theme is the struggle against the harsh environment of the Rain Village. Since it's often shown as a place full of conflict in the Naruto series. Another theme is loyalty, either to the village or to comrades.
One common theme could be their relationship development. It might explore how they get closer and the emotions involved.
Another theme is the sense of renewal. Just as rain can wash away dirt and make things fresh, in these fanfictions, the rain can mark a new beginning for their relationship. It can be a turning point from just friends to something more.
Well, I'm not sure about specific 'spirit and rain baby fanfiction' stories. You could try searching on some popular fanfiction websites like Archive of Our Own. They have a vast collection of fanfictions, and you might be able to find what you're looking for by using relevant tags.
One common theme is his potential for good or evil as a baby. Writers often explore whether he was always destined to be a villain or if there were factors that could have led him to a different path. Another theme is his relationships, like with his peers or those in authority on Cybertron when he was young.
Growth and development is another theme. Baby Riolu is at the start of its journey, so stories might focus on it getting stronger, learning new moves, and evolving. For example, it might struggle at first but through hard work and determination, it overcomes challenges and becomes more powerful.