Book of Demons: its lineage, descendants, and standing in Japan
01What this origin is
Book of Demons is a 2018 hack-and-slash by Thing Trunk in which, per its own store text, you 'wield magic cards instead of weapons' to slay the armies of darkness beneath the Old Cathedral, replacing a traditional action-RPG's skill bar with a deck of cards you build before a run and play out with a click in real time. This lineage is a comparison drawn by this site in outside critical commentary, not a connection stated by any developer whose games trace back to it here; it is the origin of the idea that a deck of cards can stand in for a weapon in real-time combat, while dodging and parrying stay a matter of the player's own reflexes rather than another card to draw.
02Sources
03Buried gems that carry this root
Code Reactors Buried gem
Per Steam's own listing, the sorceress girl Himari wanders into a world created by five witches and, together with a devil girl named Eve, descends into dungeons to unravel the mystery of the world's 'first magic.' It fuses deckbuilding with 2D action: casting a spell takes no complex command, just building a deck of 'spell cards' suited to the fight ahead and releasing it with a single button, though timing that release against an enemy's opening is entirely up to you, with a fire deck for burn damage over time, a lightning deck for raised critical rates, and an ice deck for freezing enemies before a heavy finisher. Each dungeon run reshuffles the layout, the cards on offer, and the enemies, and 'relics' can synergize into combos strong enough to break the game's own balance by design, while attack stays deck-driven but defense and dodging remain entirely a matter of the player's own reflexes, reading enemy patterns for a just-in-time dodge or parry. Made by the solo developer Studio Act One, working under the handle おにどら (Onidora), and published by Waku Waku Games, a one-person independent publisher based in Tokyo's Shinagawa ward, it began as a 2023 CAMPFIRE crowdfunding campaign that set out to raise ¥300,000 and drew ¥1,015,000 from 108 backers; on that same campaign page, in the creator's own words, 'I'd been making a living through SES contract systems-development work, but now I'm burning through savings to focus fully on making this game.' Released February 12, 2025 at ¥1,800, it is Positive at about 91 percent over 33 reviews (30 positive, 3 negative per Steam's own review API), a paid title, not free, fully launched and not in Early Access, with no AI-generated assets, and per Steam's own content descriptors, nothing sexual. It supports English, Japanese, and Simplified and Traditional Chinese, and only about 5 of its 33 reviews, some 15 percent, are in English, leaving it still largely unfound outside Japan more than a year after release.