Hajime Aikawa is the human identity assumed by the Joker Undead, a powerful and ancient being who serves as the central figure of the alternate story presented in the theatrical film Kamen Rider Blade: Missing Ace. As the Joker, his nature is fundamentally tied to the Battle Fight, a ritual where the last surviving Undead wins the right to reshape the world. If the Joker were to be the sole victor, the world would be automatically destroyed. To avoid his destructive impulses, Hajime uses the power of sealed Undead cards to take on other forms, most notably that of Kamen Rider Chalice, which is a mimicry of the Mantis Undead. He also uses the Spirit card to maintain his human appearance.

In this specific timeline, Hajime's role is defined by a tragic conclusion to the original conflict. He was sealed away by the Kamen Rider Blade, Kazuma Kenzaki, as a direct result of the Battle Fight, remaining imprisoned for four years. His personality, while still carrying the weight of his monstrous origins, is largely defined by his bond with a young girl named Amane Kurihara. He had promised her dying father, a photographer who was inadvertently killed in a skirmish involving Hajime, that he would protect the man's family. He lives with Amane and her mother, working as a freelance photographer, and shows a notably warmer and more protective attitude towards them compared to his typically distant and cold demeanor towards others.

The story of Missing Ace unfolds when the Albino Joker, another powerful Undead, threatens Amane. Realizing the danger, Leangle is forced to unseal Hajime so he can protect her. This act brings him back into the fold to fight alongside the other Riders. His primary motivation becomes the safety of Amane, leading to his ultimate sacrifice. In order to save Amane from being used as a sacrifice to empower the ultimate enemy, Jashin 14, Hajime willingly takes her place. He exchanges his own life for hers, giving the other Riders a chance to defeat the monster. After his death, his spirit is shown watching over Amane, with Kenzaki reassuring her that Hajime will always be there for her.

As a fighter, Kamen Rider Chalice is distinct from the other Riders who use the BOARD system. Because he is an Undead mimicking a Mantis Undead, his transformation is organic rather than technological, making him a "lethal adversary" whose base abilities are generally superior in agility and power to the standard forms of the other Riders. He wields the Chalice Arrow, a weapon that functions as both a bow and a double-bladed sword, and can use various Rouze Cards to perform special attacks like the spinning kick Spinning Attack or the vine-based Plant Bio. His most powerful form is Wild Chalice, accessed by using the Evolution Paradoxa card, which fuses him with all the cards in his suit and grants him power comparable to Blade's King Form while also helping to suppress his dangerous Joker instincts. In his human form, he has no special abilities, but as the Joker Undead, his true form is a towering, monstrous figure representing death.