I'm not entirely sure specifically what 'suki suki visual novel' is about as there could be many different visual novels with this name. It might be a story about love and relationships, as'suki' means 'like' or 'love' in Japanese. Maybe it involves the experiences and emotions of the characters in a fictional world.
Toph's age in the comics can be a bit ambiguous. Different comic series might portray her at different stages of her life. Generally, though, she's often shown as being in her youth, with her age ranging from around 12 to 20, depending on the context.
Toph fanfic generally involves the character Toph. Some fanfics could be about her training new earthbenders, passing on her unique skills and tough - love teaching style. Others might be about her dealing with the challenges of being a blind person in a world that often relies on sight, but she overcomes these with her incredible earthbending abilities and sharp other senses.
One interesting toph crossover fanfiction could be a crossover with the Avatar: The Last Airbender and Harry Potter universes. Toph could be a new kind of earth - bending wizard, using her skills in Hogwarts in unique ways like creating earth barriers during duels. Another could be a crossover with the Star Wars universe, where Toph's earth - sensing abilities are similar to the Force - like sensing the movements of ships or the ground composition of different planets. There could also be a crossover with the Lord of the Rings world, where Toph helps in the battles against Sauron by using her earth - bending to create fortifications and traps.
The main characters are obviously Toph and Ozai. Toph, the blind earthbender, is known for her strong will and unique way of sensing the world. Ozai, on the other hand, is a complex and often villainous character. In this fanfiction, their personalities and abilities are likely to be explored in new and different ways.
In a 'Zuko meets Toph' fanfiction, they might start off on the wrong foot. Zuko's serious and brooding nature could clash with Toph's brash and independent attitude. Maybe they get into a small fight at first, but then gradually come to respect each other as they realize they both have a strong sense of justice. For example, they could team up to take on a group of bandits that are causing trouble in a village.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics, and you can search specifically for Toph - related ones. There are also some dedicated Avatar: The Last Airbender fan sites that might have great Toph fanfic.