The 1st season of Legend of the Galactic Heroes ends with both Yang and Reinhard in positions of extreme power. Yang, as commander of Iserlohn Fortress and its stationed fleet, oversees the single largest concentration of military force in the Alliance. Reinhard, as supreme commander of the Empire's military and Prime Minister, rules the Empire in everything except name.
There the resemblance ends. While Yang may not have as much absolute power as Reinhard, he is far more "complete" and content as a person. Reinhard has lost everything he ever truly cared about in his climb for power over known space. The only person he calls friend dies as a result of Reinhard's own error in forcing Kircheis to disarm before the fateful ceremony. His guilt over this and their final argument over the Westerland massacre torment him for arguably the rest of the series. His estrangement with his sister is further trauma. She was the original purpose for his ambition and besides Kircheis, the only other person that he opens himself up to.
In the 2nd season, a personality change is quite noticeable in Reinhard. He goes through the motions of ruling and gaining ever more power, but you can see it's only an empty gesture, for he has nothing really left to him except power. With no true family or friends, his annoyance with Yang develops into a full-fledged obsession with finding ever more powerful opponents and defeating them. Conflict and war become the driving force behind Reinhard now. The Fortress-to-Fortress battle, the Imperial offensive of Operation Ragnarok, and the battle against Yang at Starzone Vermillion all stem from Reinhard's continued but ever more sterile and meaningless climb toward the throne of the Empire.