Shinichiro Nakagami is an everyday high school student, with the exception of having his beautiful and athletic childhood friend Hiromi Yuasa living in his household after the death of her parents. Unfortunately, their relationship is cold at best - Shinichiro can tell that she is suffering, but she acts coldly and distant from her foster family and so he is unable to help ease her sadness. His family is also forcing him to practice a traditional Japanese dance that does not interest him, adding to his frustration. On top of that, he is cursed to misfortune by another girl in school, the eccentric Noe Isurugi. Shinichiro juggles all of these problems on a day-to-day basis as he learns about love and the sadness of those around him.
On Planet Zi, in Blue City, a boy named R.D. works as a delivery boy for the Mach Storm team; he pilots his Liger Zero to help with his job-related tasks, but often finds himself in the middle of a Zoid battle as well. However, R.D.’s personal mission is to find the Alpha Zoid, the legendary machine that his father spent his lifetime trying to find. Along the path to fulfilling his dream, R.D. must deal with rivals such as Blake and the Savage Hammer team, and also somehow figure out the secrets of the Fuzor Zoids!
Both of these anime are about individual mecha fusing together to become more powerful, and there’s always an expected battle each episode. Another similarity is when certain, unfortunate conditions are met during combat, the union of the mecha will fail and result in its separation; and in order to perform the union in the first place, there are also prerequisites.