Hitsujirō Munakata is Souta Munakata's grandfather and a former Closer tasked with sealing destructive supernatural entities called Worms to prevent earthquakes. He lost his right arm during his Closer duties. During the 2011 Great Earthquake, he wielded the keystone Sadaijin to stab and seal a Worm beneath Tokyo's underground ruins, averting catastrophe.

Hospitalized by 2023, Hitsujirō was physically unable to aid Souta against a new Worm threat in Tokyo. Suzume Iwato visited him, reporting Souta's transformation into a keystone and imprisonment in the Ever-After. Initially advising Suzume to accept Souta's fate, he offered critical guidance after seeing her resolve. He revealed her ability to perceive the Ever-After and the Worm meant she had once entered that realm through a specific door. He instructed her to find that original door, located in the ruins of her childhood home in Tōhoku, as the sole way for a mortal to re-enter the Ever-After and attempt Souta's rescue.

After Suzume departed, Sadaijin appeared at his hospital window. Hitsujirō acknowledged the keystone's release from duty and asked it to watch over Suzume. His relationship with Souta was one of strict mentorship; Souta's earlier reluctance to seek his help stemmed from not wishing to disappoint him, reflecting Hitsujirō's high expectations for his grandson in their shared duty. The name "Hitsujirō" incorporates the character for "sheep" (羊), while "Munakata" references the Three Munakata Goddesses (宗像三女神) from Japanese mythology, deities born from the shattered Sword of Totsuka and associated with the sea.