Moon A very specific part of the ending of Animorphs messed me up as a child, and I still think about it to this day. Spoilers for book 54 of Animorphs lol
Jake, who is generally considered the leader, and a few other Animorphs get on a spaceship to rescue an alien that got captured. They do not bring Cassie, Jake’s love interest. Because of theory of relativity and the speed of the ship (I guess?) as they are in space Jake mentions that after 15 minutes had passed on the ship would have been something like 60 years on Earth, and Cassie has probably grown old, gotten married, and had children/grandchildren. His thoughts get interrupted when Marco, another Animorph, suggests they watch a movie to pass the time. It was heartwrenching to me, a young kid, to think of her mortality and how life would go on for everyone else.
Weird series, but there are some really good moments that have stuck with me for a long time.
Edit: how do you blur spoilers?