Since I don't know who Cris and Joana are exactly, it's really difficult to tell their full story. Maybe they are characters from a local story in a particular region, or they could be two ordinary people with a story known only to those close to them.
One possible story could be that Cris and Joana are childhood friends. They grew up in a small town. Cris was always more adventurous and Joana was the shy and studious one. As they grew older, Cris convinced Joana to go on a trip around the country with him. During the trip, they faced many challenges but also discovered new things about themselves and their friendship grew stronger.
I don't know the exact 'Cris Soto Joana fanfic', but generally in fanfics, there can be themes related to the characters' backstories. For Cris and Joana, perhaps there are themes about their families, their past traumas, and how they heal and grow. Also, if they are in a particular setting like a school or a workplace, themes about competition and cooperation might be present.
I haven't come across 'Cris Soto Joana fanfic' myself. But usually, to find fanfics about specific characters, you can also check out relevant fan communities on social media platforms. Sometimes fans share their works or know where to find them. Maybe start by looking for groups dedicated to the source material that these characters might be from.
First, start with the basic outline of his body and head. Then, add details like his shield and costume features. Pay attention to his facial expressions and musculature.
One common theme could be the joy and excitement of gift-giving. Another might be the decoration of the party space with colorful lights and ornaments.
Common themes include self-discovery and the challenges of adapting to a different physical form. Tropes might involve misunderstandings between the swapped characters and the reactions of those around them. Also, there's often a lesson learned about empathy and seeing things from another's perspective.