Playing of the Demon Lord Who Found Spare Time Unmanageable

is chapter 12 of the Beelzebub manga.

Summary
At home in his room, Tatsumi realizes the Zebub spell on his arm had retracted and celebrates. Hildegarda enters carrying a pile of boxes wondering what happened. Tatsumi tells her that after a week of nothing but video gaming, he had figured out that staying docile retracts the Zebub spell across his arm. Hearing this, Hildegarda stomps on his video game console and calls Tatsumi a NEET. Tatsumi angrily demands his Mildrath, Deathtamoor and Orgodemir be returned. Hildegarda claims she has a better toy waiting for him, one that she brought from Hell. Tatsumi helps Hildegarda set up the toy.

After nearly finishing the toy, now resembling the edges of a box, Tatsumi asks Hildegarda what they are making. Hildegarda refers to the unclear instruction manual, but finds that it’s some sort of playpen. Tatsumi finds the last part and attaches it. A veil surrounds Hildegarda and Tatsumi by the sides of the box, trapping the two in. Hildegarda calmly indicates they’ve been sealed, to which Tatsumi reacts in irritation. Hildegarda explains that, according to the instruction manual, they are trapped in a cage used to capture demon beasts in the wild. The cage is apparently made of demonstone, a material that is supposed to prevent beasts from escaping, and can only be unlocked by playing with a shape sorter (designed for kids) and fitting in a set of blocks correctly. The instruction manual proceeds to taunt the reader, claiming the cage will never open, and finally tell the reader to construct the cage from the outside, with a little “laugh” in brackets at the end. With no option but to call for Beelzebub to solve the shape sorter, the two bang on the veil of the cage and wake him up. They try to speak with him, but the veil is sound-proof. Responding to Tatsumi and Hildegarda, Beelzebub bows, then rolls back and forth on the floor. Finally, he spots the shape sorter. He picks up the circular block and pretends to place it under the bed to make a ploy before putting it in the shape sorter. Unfortunately, he tries to put it through the triangular hole. Unable to put the circular block in the triangular hole, he tries to thrust it in, but the shape sorter breaks apart. Scared of staying trapped forever inside the cage, Tatsumi becomes enraged and tries to break it open, somehow drawing out demonic power from Beelzebub even though Tatsumi isn’t touching him. He manages to break the cage open and feels satisfied destroying it. Hildegarda is satisfied too, as the Zebub seal has returned across his arm, to Tatsumi’s chagrin.

At Ishiyama High, Aoi is walking outside the school in front of students from the floors above, whom have found that she had returned from northern Kantō. Having been told by two of her underlings about Tatsumi beating Hajime and Tatsuya, she wonders what kind of man he is.

VOMIC adaptation
A VOMIC adaptation of the chapter was aired through the second half of September 2010, starring the same cast as used in the anime series.

Trivia

 * The chapter references an act by Japanese comedy duo Monster Engine entitled.