Henry 1.0

Henry 1.0 is Leviathan's long lost pet snake that mysteriously went missing as a snakelet. Its first appearance was in Lesson 7-17.

Story
Note: this section may include spoilers

Main Story
In Nightbringer Lesson 1-14, Asmodeus buys some bufo toad-flavored inferno ice cream. Mammon finishes it and the ice cream stick has the words "Winner" on it. A summoning circle suddenly appears above the stick and a giant serpent is summoned. The serpent then proceeds to chase after them. In Nightbringer Lesson 1-15, it is revealed that it was part of "The Pandora's Box Promotion" for inferno ice cream and the prize was a randomly generated rare magical creature. Asmodeus ended up throwing a muffin that Solomon had made into its mouth and made it faint. In Nightbringer Lesson 2-1, Leviathan says he found the snake while it was running away for dear life from Satan inside the House of Lamentation and decided to save it. It is unknown how the snake ended up there though. Solomon ended up shrinking the snake since it was blocking his way. In the end, Leviathan decided to keep the snake as his pet. As he had not decided on a name for the snake, Leviathan just referred to the snake as "Snake" or "Snake-chan". In Nightbringer Lesson 15-13, Leviathan ended up naming the snake "Henry" after the main character of The Tale of the Seven Lords.

MC, Mammon, Leviathan, Beelzebub, Asmodeus, and Solomon were sucked into a portrait of one of Asmodeus's ex-lovers in the Demon Lord's Castle and teleported to the underground labyrinth, where they came across Henry 1.0. Although Leviathan recognized Henry 1.0 on sight, the snake seemed to have no recollection of its previous owner, and tried to attack them. The group was able to escape when Solomon amplifies Asmodeus's powers to charm Henry 1.0.