Ishaku (「イッシャク (一尺)」?; Isshaku; one shaku) is a Poncle who traveled Nippon with Shiranui as the 6th Celestial Envoy. Issun is his grandson. He and Issun once argued, which was the reason why Issun left Ponc'tan to become a travelling artist.
I'm no longer the young boy you remember me as, Ammy. I've grown to become the leader of Ponc'tan. Yes, I am the legendary swordsman, Ishaku!Ishaku
From Issun's description, Ishaku sounds like a very strict person, but actually the two are very alike. However, unlike Issun, he takes his duties as a Celestial Envoy seriously. Ishaku's appearance and speech in the past (when he is briefly seen) seems very similar to Issun, including his brash and boastful nature. He also uses the same nickname for Amaterasu as Issun ("Ammy").
Being a Poncle, Ishaku is the size of an insect. He is clad in what appears to be brown samurai armor, with two large scrolls on his back and large brown helmet (seemingly made from the shell of a kabutomushi beetle), like those worn by all male Poncle. He stands about as tall as an insect and glows a bioluminescent yellow. He also has a sword called Denjinmaru, which appears to double as a brush. Ishaku's shoulder length hair and large, drooping eyebrows show his age since its colour has long since faded. He has a single wrinkle either side of his mouth that goes up to his tiny, red nose.
At some point after the Ark of Yamato crashed landed in Laochi Lake, Ishaku met the wolf-goddess Amaterasu and took on the role of the 6th Celestial Envoy. They journeyed through the land of Nippon and came to Kamiki Village. The village was terrorized by the demon Orochi, the very monster who had attacked the Celestial Plain, Amaterasu's former home. He had been demanding a maiden as sacrifice once every year since he had taken up residence in the nearby Moon Cave. The people of Kamiki Village saw Amaterasu and mistook her for a familiar of Orochi. They gave her the name Shiranui and hid from her when she went on her nightly patrols to guard the village. That year Orochi chose the maiden Nami as his sacrifice, causing the village's warrior, Nagi to take up arms and protect the woman he loved. The warrior did battle with Orochi and to his surprise was aided by Shiranui. The wolf used many strange powers in the struggle with Orochi and fought valiantly alongside Nagi. When the battle seemed all but lost Shiranui howled to the sky, causing the moon to appear and re-energize Nagi. With a final attack Nagi defeated the beast and saved the people of Kamiki Village. The victory did not come without sacrifice. Shiranui had been injured and was infected with Orochi's venom. Nagi carried his new comrade back to the village where he told the people of Shiranui's noble sacrifice. Shiranui passed away quietly, ending Ishaku's journey.
Ishaku continued his duty as Celestial Envoy, telling all of Shiranui's deeds. Eventually he returned to Ponc'tan and fathered at least one child. Some time later he took his grandson Issun as his apprentice. He wanted the boy, who had more talent then any of the other Poncles, to follow in his footsteps and taught him everything he knew. Issun believed that Ishaku was too hard on him and eventually left the village in an effort to prove himself. During his exit, it was revealed that Issun stole one of Ishaku's drawings of a wood sprite (which he made at somepoint before returning to Ponc'tan, when Sakuya had a more adult appearance). Ishaku, believing he had failed as Issun's master, remained in the village, awaiting the day his grandson might return.
Amaterasu encounters Ishaku in Ponc'tan while looking for information about Lika. Ishaku seems overjoyed that Amaterasu has returned and gives her Praise, but does not give her much information. If Ishaku is talked to again after Amaterasu discovers that Lika went through the Spirit Gate, he tells her only he can open it and warns her about it (probably because he remembers what happened the last time she went through the gate). He was one of those who recieved Issun's work when he was travelling around Nippon after Amaterasu went into the Ark of Yamato to gather enough praise to restore and empower her, so she could fight Yami, he was proud of Issun, admitting that he was a better Celestial Envoy than himself could ever be .
A younger Ishaku is seen at the end of the True Orochi battle and is also mentioned and seen after Lechku & Nechku's battle. In his second appearance, he is not actually seen but is depicted in the images which show after the battle.
After Akuro flees into the past to bathe in Orochi's blood, Chibiterasu goes back in time to stop him and eventually travels back 100 years before the events of Ōkami. In this time era, Chibiterasu and Manpuku encounter Ishaku and Shiranui, freeing them from being trapped in ice in Orochi's Ice Room. Ishaku acts as Shiranui's mouth, so what he says can be understood. Although he seems distrustful of Chibiterasu, Ishaku seems reassured, although slightly confused, when Shiranui tells him that Chibiterasu is its grandson. When Akuro succeeds in bathing in Orochi's blood, Chibiterasu enters the Dark Realm to stop him, and Ishaku follows, opening a crack in space, allowing Nanami, Manpuku and Kagu to assist Chibiterasu. Later, when he confronts Akuro, then Dark Chibiterasu, Ishaku is Chibiterasu's partner during the battles. After Akuro's defeat, he stays in the past.
- It is heavily implied that the Travel Guides were written by Ishaku, through the text contained in said guides and his signature on some of the images. Additionally, the image of his younger form (the same depiction shown after the Lechku & Nechku battle) appears in the background of the Travel Guide menu.
- Oddly, in the Wawku Shrine right before the Lechku & Nechku battle, Oki claims that he left the wounded Shiranui in the younger Ishaku's care. However, if Ammy goes back to where Shiranui is right before the battle, Oki is gone but Ishaku is nowhere to be seen and only appears later. It is unknown why this is, but it could be that the developers overlooked this detail, since it is unlikely that players will want to return to Shiranui's area right before the boss fight.
- Ishaku's luminescence is a yellowish-brown colour.
- Ishaku's name is rendered as Isshaku in Ōkamiden.
- Despite being one of the two currently living Celestial Envoy, Ishaku had never seen to use a Celestial Brush technique.
- Ishaku's name, meaning one shaku (a traditional Japanese unit equal to about 30 cm or 1 foot), is a play on Issun's name which means one sun (a unit equal to one tenth of a shaku).