Daichi, who initially appears as a seemingly lazy young man often found lounging by a pool in a hat, is the human form of the Elephant Undead. As the Category Jack of Clubs, he is a high-ranking Undead whose true form is an immense, elephant-like monster. Despite his relaxed human disguise, he possesses overwhelming physical strength and a surprisingly prudent and strategic mind, preferring to avoid conflict until he has gathered sufficient information on his opponents.

Daichi's personality is defined by a strategic patience that borders on pacifism, though it is rooted in pragmatism rather than a true love of peace. He finds unnecessary fighting to be a nuisance and is content to observe the Battle Fight from a distance, waiting for the ideal moment to strike. His primary motivation is to win the Battle Fight by exploiting the confusion and exhaustion of others. He believes it is pointless to engage an enemy without knowing the full limits of their ability, so he spends much of his time analyzing the skills of the Kamen Riders and other Undead. This calculated approach makes him a formidable threat; other Undead, including the powerful Category Queen Orchid Undead, are known to fear him and avoid direct confrontation. However, this apathetic demeanor shifts dramatically if another Undead encroaches upon what he considers his territory, provoking him to unleash his full, devastating fury.

Within the story, Daichi serves as a major obstacle for the Riders, demonstrating the vast power gap between standard foes and high-ranking Undead. His role is to force the heroes to achieve a new level of strength, as he cannot be defeated by their normal forms. His key relationships are primarily antagonistic. He briefly comes into conflict with Hajime Aikawa, the Joker who transforms into Kamen Rider Chalice. Upon recognizing Hajime's belt and realizing he is the Joker, Daichi opts to postpone the fight, recognizing the unique threat the Joker represents. His most significant confrontation is with Kazuma Kenzaki, Kamen Rider Blade. After running repeated mental battle simulations, Daichi becomes convinced he has a one hundred percent chance of victory against all four Riders simultaneously. He then rampages through the city to draw them out, and in the ensuing battle, he lives up to his calculations, easily overwhelming Kamen Rider Garren and Leangle and shattering Blade's mask with a single blow. This forces Blade to use the Rouse Absorber to assume his enhanced Jack Form, a transformation powerful enough to finally turn the tide and seal the Elephant Undead using the Lightning Slash technique.

Daichi's development within the series is subtle but present. He transitions from a purely observational and evasive figure to an active combatant only when he is certain of victory. His initial encounters are skirmishes to gather data, such as when he is manipulated into fighting Chalice but withdraws after confirming Hajime's Joker nature. This careful data-gathering culminates in his overconfidence, leading him to abandon his cautious strategy for a direct assault on all the Riders at once, an action that ultimately leads to his sealing. He is later unsealed by the Leangle, Mutsuki Kamijo, to help fight the powerful Kerberus Undead. In this instance, Daichi is not motivated by his own goal to win the Battle Fight but is instead an unwilling participant, fought alongside the Riders and was ultimately resealed after being defeated by the Kerberus.

In combat, the Elephant Undead wields two primary weapons: a massive spiked iron ball and chain called the Iron Boom, and a heavy hammer named Earthquake. The hammer's blows are powerful enough to crack a Kamen Rider's mask, which is forged from the near-indestructible metal Oreichalcum. He can also generate a gust of wind or use a direct strike attack known as the Nose Striker from his chest, as well as create a defensive Shield Barrier. His fighting style is a direct reflection of his personality, combining overwhelming, brute-force physical power with a patient and strategic intelligence that makes him a uniquely dangerous adversary.