"Umaru and Rock-Paper-Scissors Contest"
A huge Necolumbus cat pillow is the prize in a rock-paper-scissors tournament, and Umaru will do ANYTHING to get it, even if it means making Taihei miss work to help her accomplish her latest selfish goal, which has DIRE CONSEQUENCES for her brother.
Umaru reads a flyer for a jan-ken-pon (rock-paper-scissors) tournament, with the winning prize being a huge, long Necolumbus cat pillow. To make sure she gets it, she makes Taihei take the day off work by telling him it's an "emergency." On the day of the contest, she (as UMR) reveals what the "emergency" was by showing him the flyer. Taihei responds, "You selfish brat, you call THIS an emergency?! I had to turn down a weekend shift for this!" Umaru lies to him that she wanted him to take a break from working so hard lately, and that she wanted to play with him. Knowing he can't turn down an opportunity for them to bond, Taihei falls for the ruse. At the contest, Umaru leaves him at the first store and goes to another to increase her chances (and possibly get TWO of the cat dolls). Taihei agonizes over how gullible he is (and how GREEDY his sister is). To make matters WORSE for Taihei, when he makes it all the way to the finals, his final opponent is EBINA. After Ebina is defeated, Taihei (thinking that Ebina really wanted the pillow badly) decides to give the doll to her, in the hopes that Umaru and Ebina can stay friends. As Ebina leaves, Umaru, in a HUGE fit of SELFISH RAGE (and VERY upset that her plan failed), appears behind Taihei, and reveals that she lost early on in the tournament and came back to where Taihei was and saw him win the prize. She then berates Taihei for giving "her" Necolumbus away to Ebina, calling him a "FOUR-EYED CORPORATE SLAVE." Taihei tries to explain that it was for her own good. As an act of revenge, Umaru gets the same doll from an online auction days later (WITH HER BROTHER'S MONEY).
(Originally chapter 10 when it ran in Weekly Young Jump)