Some of the most memorable moments in the series are these.
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* Ataru's class is raising caterpillars and, despite an overly large and ugly one eating all of the food, Ataru spends the entire episode working with Lum to keep the rest of the class from hurting it, believing it will become a beautiful butterfly. At the end, it turns out to be a fairy whose first words to Lum and Ataru are, "Mama! Papa! Thank you for believing in me."
* In one season finale, Ataru mistakenly eats some food that Ran made for Rei that increased exponentially in size once inside the stomach, thus making him get incredibly sick. Lum enters an Alice in Wonderland-style realm to look for Ran to get an antidote, but Ataru's monitor flatlines before she does and Lum breaks down sobbing. [[spoiler:Fortunately, Ataru got better and the monitor was simply unplugged on his end.]]
* The most popular episode includes one where Ataru breaks down in tears in the middle of an alley, clutching a small doll that Lum left behind when she suddenly left town. [[spoiler:While she simply had to renew her passport to continue living on earth, it's the first instance where Ataru demonstrates he truly loves Lum by how much he misses her. Also, Lum bugged the doll so she was able to hear every word he said.]]
* Kitsune hears a fairy tale of a fox who defeats an Oni to rescue a girl trapped inside of a picture. When Kitsune next visits Tomobiki, one of the first things he finds is a photo of Shinobu. Having never seen a photo before, Kitsune believes she's trapped in the picture and his reaction is just heartbreaking.