(After Nanaki learns the truth about his father Seto's death in defending Cosmo Canyon)
Bugenhagen: Nanaki, I want you to continue your journey with Cloud and the others.
Red XIII: Grandpa!?
Bugenhagen: Listen, Nanaki. Cloud says they are trying to save the planet. Honestly, I don't think it can be done. For even if they stop every reactor on the planet, it's only going to postpone the inevitable. Even if they stop Sephiroth, everything will perish. But, Nanaki. I've been thinking lately. I've been thinking if there was anything WE could do. As a part of the planet, something to help a planet already in misery...No matter what happens, isn't it important to try? Am I just wishing against fate? I am too old to do anything about it...This year, I'll be 130. Ho Ho Hoooo. That is why, Nanaki, you must go with them! For my sake.
Red XIII: Grandpa...
Bugenhagen: I wanted to show you your real father before you left...I'm so glad that you came back while I was still alive to show you.
Red XIII: Grandpa... don't talk like that. I don't want to think of life... without you.....
Bugenhagen: Ho Ho Hoooo. Well, I've had a long life.
Red XIII: Grandpa! You must live! I'll see to it. I'll see to what's happening to the planet. And I'll come back to tell you.
(When Nanaki fights Sephiroth in the Planet core)
Red XIII: I'm going to see it through to the end. For our future... and that of the planet. I understand now, Grandpa. That is my mission!