Rouze Cards are obtained when an Undead has been defeated, which is indicated when their Ouroboros Buckle opens revealing what category and suit they belong to, and has been sealed away by either a Rider using a Proper Blank card, Common Blank card or the Stone of Sealing. Normally, Category 2-Queen Cards have the Ouroboros patch on the picture of the species which they resemble.
The cards are categorized into Categories, the exact same way the Undead are: Aces, the Numbers (2-10), and the Royal Club (Jacks, Queens, & Kings). They are also categorized into 4 suits: the Spades, the Diamonds, the Hearts, and the Clubs. The Joker Cards, the Wild Card and the Mighty cards used by Kamen Riders Glaive, Lance, and Larc and Vanity Card which created by Four different Category King Cards belong to none of either categories or suits.
Each Rouze Card allows the Riders access to the powers of the Undeads sealed within them. Rouze Cards need AP to be used, the amount of which is needed for the card to be used is located on the right side of the card just below the Undead's picture. Riders can gain AP by fighting an opponent while wearing their Rider suit and the amount of AP they have accumulated is gauged by a digital counter located somewhere on their weapons.
The only Cards that don't use AP are Category Ace cards, with the Royal Club Cards serving to increase a Riders' AP count. Category Joker Undeads can also use Rouze Cards to assume the form of the Undead that is sealed within the card and access all of their powers.
These card allow the Riders to transform into their suits. These Undeads were regarded as the best fighters.
These cards allow the Riders to assume Jack form when used in conjunction with an Absorb Queen Card of the same suit with the use of a Rouze Absorber. Since Hajime is the Joker Undead, he has no need for a Rouze Absorber, so his Jack Card just allows him to become the Wolf Undead.
These cards allow the Riders to use their Fusion Jack and Evolution King cards with the use of a Rouze absorber to change into their Jack and King forms. Hajime never had a Rouze Absorber so it just allows him to become the Undead sealed inside the card.
These cards allow the Riders to assume King form when used in conjunction with an Absorb Queen Card of the same suit with the use of a Rouze Absorber. For Hajime, it allowed him to fuse with all of his cards and assume Wild Form. For Mutsuki, it instead allowed him to become the Undead himself, morphing between his human form and the Undead's form.
Evolution Caucasus: Allows Blade to assume King Form
Evolution Giraffa: Allows Garren to assume King Form (Never Used)
Evolution Paradoxa: Allows Chalice to assume Wild Chalice (if all Suit of Hearts Rouze Card seals are completely collected) or transform into the Paradoxa Undead (if one or more Suit of Hearts Rouze Card seals are missing)
Evolution Tarantula: Allows Leangle to assume King Form (Only used to become Tarantula Undead to fight and reseal the Spider Undead)
When Kamen Rider Blade initiates King Form, his Rouze Cards change their appearance and their AP Cost will increase. In addition, their cards are fused with the Kamen Rider to form armor, allowing him to call upon that Card's power without needing the Blay Rouzer to do so.
The Rouze Cards are similar to the Clow Cards from Cardcaptor Sakura, both being creatures that turn into cards after being defeated and sealed by the shows main heroes and being used by the heroes as the show progresses.