Blade Fangs was a Japanese manga created by Itagaki Keisuke. There were four works in total, namely Grappler Blade Fangs, Fanma Blade Fangs, Blade Fangs Path, and Blade Fangs Path 2. The theme of this manga was hand-to-hand combat, and it told the story of the young Blade Fang fighting with strong enemies in various underground arena competitions. The characters in the Blade Fangs series had distinct personalities, compact storylines, and unique styles. This series of comics was well-known in China and was welcomed and loved. The animated version of Blade Fangs also had two seasons and could be watched online. As for the viewing order of Blade Fangs, they could be viewed in the order of Blade Fangs 1, Blade Fangs 2, Fanma Blade Fangs, Blade Fangs Path, and Blade Fangs Path 2.
One aspect to consider in this fanfiction could be the power dynamics. If Yuichiro is dominant, it might lead to interesting character interactions with Mikaela. For example, Yuichiro could be the one making decisions in their adventures together, while Mikaela might play a more supportive role. It also adds an element of tension and drama to their relationship, as the dominant - submissive dynamic can create various scenarios for character growth and conflict.
One common theme is the deep emotional bond between them. Given their relationship in the original work, fanfictions often explore how they support and care for each other on a more profound level. Another theme could be adventure, where they go on quests together and their relationship develops during those experiences.
I'm not that familiar with 'yuichiro hyakyua' crossover fanfiction, but often in crossovers, themes like friendship between characters from different worlds can be common. Maybe also the exploration of different powers or abilities when the characters interact.
Survival is also a big theme. When he is in a crossover with a more dangerous world, like a post - apocalyptic or a world full of powerful enemies, Yuichiro has to use his skills and wits to stay alive. It creates a lot of tense and exciting moments in the fanfiction.