Kōjirō Shindō is a 30-year-old master negotiator and the chief officer of the United Nations Policy Division at the Ministry of Foreign Affairs in Japan. He holds the rank of chief Secretariat officer in the Ministry's United Nations Policy Division. Prior to the central events of the story, he worked for the Ministry of Internal Affairs and Communications in Kasumigaseki, where he demonstrated his negotiation skills during a land acquisition case involving a plating factory in Sagamihara City. Shindō has a well-earned reputation as a tough negotiator who has resolved numerous challenging issues throughout his career. He is known for his cool-headed and rational demeanor, and he approaches every negotiation with a philosophy of considering the positions and interests of both parties involved. This balanced approach has earned him the trust of both his subordinates and his superiors.

Shindō's core motivation stems from his belief in the value of dialogue and mutual understanding. He is fundamentally driven to find solutions that serve the interests of all sides, a principle that guides his actions throughout the story. When he and his colleague Shun Hanamori are absorbed into the mysterious giant cube known as Kado, which materialized at Haneda International Airport and swallowed their plane along with 252 passengers, Shindō becomes the first human to make contact with Yaha-kui zaShunina, an otherworldly being from a higher dimensional universe called Novo. Yaha-kui zaShunina materializes in the form of a human and expresses a desire to advance the world by introducing a series of mysterious devices to humanity. Despite the initial uncertainty and potential threat, Shindō chooses to become the primary liaison and negotiator for this alien entity, bridging the gap between humanity and the anisotropic being.

Shindō's role in the story is that of a mediator and representative. He negotiates on behalf of Yaha-kui zaShunina with the Japanese government, which is initially cautious and fearful of the unknown entity. The Japanese government sends its own negotiator, Saraka Tsukai, to represent their interests, and Shindō works alongside her as the situation unfolds. As Yaha-kui zaShunina introduces advanced technologies to humanity, starting with an endless energy source called Wam, followed by the sleep-eliminating Sansa, and finally the gravity, inertia, and mass-controlling Nanomisheim, the world becomes increasingly divided and pressured. The United States and other major powers demand that Japan hand over the technologies to the United Nations, fearing global imbalance. Shindō navigates these political pressures while trying to maintain the trust of both Yaha-kui zaShunina and the human governments.

Key relationships in Shindō's life include his close colleague and junior Shun Hanamori, who works as his subordinate and later plays a crucial role in protecting Shindō's daughter. He is also close to his university classmates Shuhei Asano, who works for the National Public Safety Commission, and Ritsu Natsume, who works for the Cabinet Secretariat's National Security Bureau. Both of these friends coordinate with him as the crisis evolves. Shindō develops a complex relationship with Saraka Tsukai, who is later revealed to be a reincarnation of an anisotropic being who entered the human world long ago. Saraka initially distrusts Yaha-kui zaShunina and is determined to protect humanity and the Earth from the entity's unknown intentions. Over time, Shindō comes to understand her perspective while maintaining his own commitment to dialogue. He also forms a significant bond with Yaha-kui zaShunina himself, becoming the first human to truly understand the entity. Shindō even gives the being a paper-seahorse bookmark, which becomes a symbolic representation of their connection.

Shindō's development throughout the series is profound. Starting as a consummate professional negotiator who believes in rational problem-solving, he is gradually exposed to concepts beyond human understanding. As Yaha-kui zaShunina reveals that its ultimate goal is to take humanity to the anisotropic universe, Shindō faces an impossible choice: to progress beyond human form or to preserve humanity's existing existence and dignity. When he resists this proposal, Yaha-kui zaShunina attacks him, but Saraka intervenes, revealing her true nature. Shindō is gravely injured but is resurrected through Saraka's abilities. Together with Saraka, he devises a plan to stop Yaha-kui zaShunina by creating a device that can neutralize the fregonics field that protects the Kado. He commissions the construction of a special vest and arm covers from the Osakabe Plating Factory, designed by physicist Kanata Shinawa. In the final confrontation, Shindō faces Yaha-kui zaShunina and refuses the offer to go to the anisotropic universe. Yaha-kui zaShunina kills him, but Shindō's daughter, Yukika, who was born from his relationship with Saraka and raised by Shun Hanamori in a time-shifted space, returns to defeat Yaha-kui zaShunina and nullify all the advanced technologies, restoring the world to normal.

Notable abilities include his exceptional negotiation and communication skills, which allow him to handle complex and unprecedented situations involving a being from another dimension. He is a strategic thinker who can see multiple perspectives and find common ground between opposing positions. He is also a capable planner and coordinator, as shown when he organizes the response to the crisis by working with government agencies, scientists, and international bodies. Additionally, Shindō has a personal fondness for origami, and he often folds paper animals when he is thinking or in idle moments, a detail that reflects his methodical and contemplative nature. His unwavering commitment to finding a peaceful solution that respects both human autonomy and the anisotropic entity's desire for connection defines his ultimate legacy.