Anything with Jean and Scott, but especially the infamous mesa sequence.
This story arc introduces Kitty Pryde, then a 13-year-old girl who has just learned she can go through solid objects. By the third issue of the story, Kitty has been on the run from the Hellfire Club for 13 hours straight, and is exhausted, bruised, and terrified. After Phoenix stops her pursuers with extreme prejudice, she runs away again, but this time Jean follows her...shifting from her Phoenix garb into normal early-1980s civilian garb. Kitty collapses into Jean's arms and sobs out her relief while Phoenix — the woman who just destroyed a car and badly injured or killed its occupants — simply hugs her and soothes her. It's one of the last really tender moments Jean displays before the end.