Pigmo (ぴぐも, Pigumo) is an old acquaintance of Lum.
When Lum was in kindergarten, he got turned into a frog by playing a dangerous yet popular game in which two persons put a cursed wildgrass on their heads and shout to each other to become something, and whoever shouts the loudest wins remaining as he/she and turning the other into what he/she wanted to become. Only by receiving a kiss from the one he loves the most can the spell be removed, and Lum accepted to kiss him.
Years later, he reunites with an old friend of his, and as they speak of old times they replay the spell game in which he loses and turns into a frog again. Three days later, he is delivered in a box through space mail to Lum in Tomobiki High School, for she is still the one he loves the most, but as she didn’t remember his name, she gets annoyed by his request to kiss him and tosses the frog out the window. Shortly after however, she remembers and apologizes to him when he returns in class 2-4 and drives Mendō to nearly jump out the window upon proving with pictures of his true appearance that he’s not as ugly as he is pathetic after revealing how he turned into a frog again. Lum was however reluctant into kissing him again with her darling around but eventually does it after Ataru hits him, and upon turning back to his original appearance, everyone is surprised to see he’s actually as tiny as a person’s hand.