Well, 'photo kano visual novel' is probably a story - driven experience where the visual aspect is important, just like other visual novels. Maybe it has a unique art style to depict the world of photography. It could be about a young photographer's journey, his or her growth in the field of photography, and the relationships that are formed through the shared passion for photography.
A fanfiction might explore a scenario where Kido and Kano have to work together to face a new threat in Mekakucity. Kido's calm and collected nature could complement Kano's more mischievous but also resourceful personality. They might start off bickering but as the situation gets more serious, they realize how much they rely on each other and develop a newfound respect.
Since I don't have detailed knowledge of the 'photo kano visual novel', I can't give a definite answer. Generally, if it adheres to common standards of family - friendly content such as having a positive message, no inappropriate images or text, it could be suitable for all ages. However, some visual novels are designed with a more mature audience in mind, so it's important to look into reviews or more information about it.
One common theme is friendship development. Since they have different personalities, seeing how their friendship grows is a popular topic. For example, in many fanfics, they start as acquaintances and gradually become close friends.
One theme could be trust. Since they are part of the Mekakucity Actors, they need to trust each other with their secrets and powers. A fanfiction could explore how they build that trust over time.
One common theme is the exploration of their unspoken feelings. Since they both have complex personalities in the Kagerou Project, fanfictions often focus on how they might be hiding their true emotions for each other.
One idea could be that they go on an adventure together in a magical world. They might face various challenges and have to rely on each other's unique abilities to succeed.
First, understand the characters well. Know their personalities, strengths, and weaknesses. For example, Kido is often seen as a strong leader, so make sure to incorporate that in the story. Then, come up with an engaging plot. It could be something simple like them spending a day together and learning new things about each other.