Complex sentence: He rescues a couple of young children named Bat and Lin from bandits and allies himself with another "Nanto Seiken" master named Rei, who is searching for his kidnapped sister Airi.
Split into simpler sentences: He rescues a couple of young children named Bat and Lin from bandits. Afterwards he allies himself with another martial artist named Rei, a "Nanto Seiken" master who is searching for his sister Airi.