Kai Hiwatari from anime series, Beyblade, and Seto Kaiba from anime series, Yu-Gi-Oh, are two characters that are at first, wouldn't be alike, but if you look at them closely, they're so much alike.

For example, they have a relative who is an antagonist to them; Kai has his grandfather, Voltaire, and Kaiba has his stepfather, Gozaburo. The point is, Voltaire and Gozaburo only care for power and that they have manipulated both Kai and Kaiba into making use of them. They're both deep, dark characters, and half of the time, they're antagonists, but on the other half, they're protagonists. Both have a calm personality and are loners.

They have their differences as well such as Kai's goal is to run the military company, Hiwatari Enterprise, as its heir, while Kaiba's goal is to become the world's greatest player in Duel Monsters. The former's age is around fourteen to sixteen years old, while the latter's age is around eighteen years old. Kai uses a Beyblade with a Bot-Beast named Dranzer in battle, but Kaiba uses Duel Monsters with his favorite card, Blue-Eyes White Dragon.

This would give out a conclusion that Kai and Kaiba are so much alike, despite having differences. In fact, I've been wondering if Takao Aoki has gotten ideas for Kai from Kaiba, whose creator is Kazuki Takahashi. Also, Kai's relationships with Tyson Granger, Max Tate, and Ray Kon could be compared to Kaiba's relationships with Yugi Muto, Joey Wheeler, and Tristan Taylor. Lastly, their names have "Kai-" written all over so that could be a possibility of where the ideas for Kai have come from. Although not much interest, Kai and Kaiba are most important characters because they're so much alike and different.