"I'm sorry," Sephiroth says - not so much apologizing for any of his own actions, Mithrun's been clear enough that he hasn't really misstepped here, but for his inability to help Mithrun with what's distressing him. Because he really doesn't think there's anything he can do here, exactly. Even his own success felt less like a product of his enhanced abilities - which are far less enhanced here than they have ever been at any other point in his life - and more just luck. He can't exactly offer Mithrun tips or advice, and he isn't sure that wouldn't just make Mithrun gloomier.

Well, if he doesn't know what he could possibly do here...perhaps Mithrun does. "Is there anything I can do?"