WARNING: The following contains spoilers for One Piece Chapter #1020, "Robin vs. Black Maria," by Eiichiro Oda, Stephen Paul, and Vanessa Satone, available in English via Manga Plus and Viz Media.
After the reveal of Yamato's Devil Fruit transformation in Chapter #1019 of One Piece, there was plenty of fan speculation about what animal his form was based on. Mythical Zoan-type Devil Fruits leave a lot to the imagination, but with Chapter #1020 continuing the face-off between Yamato and his father, Kaido, we finally get a concrete answer.
The Devil Fruit that Kaido had sought after and Yamato ended up consuming by accident is the Mythical Zoan-type Dog-Dog Fruit Model: Okuchi-no-Makami, based on the divine wolf from Japanese folklore. Within the context of Wano, they are considered a guardian spirit, fitting for someone like Yamato, who wants to take the place of Wano's greatest protector, Oden. It's this fact that upsets Kaido, seeing this power used against him by his own child to protect the country he's trying to control.
Yamato is determined to liberate Wano and its people from Kaido's grasp and will open its borders the way Oden always intended. He then unleashes the breath attack "Namuji Glacier Fang," which clashes with Kaido's Blast Breath in an explosive collision.
There's a surprising amount to be learned from the reveal of Yamato's hybrid form. Okuchi-no-Makami were pure-hearted wolf deities that could speak to humans, bring good luck and protect crops from wild animals. They were also known to protect people from evil, however, the worship of Okuchi-no-Makami dwindled as the Japanese wolf population went extinct in the 1900s due to systematic hunting and rampant disease.
Considered a guardian deity in Japan, Yamato couldn't have a more fitting Devil Fruit form. Yamato denounced all relation to his father and even took the name of the hero of Wano, Kozuki Oden, even vowing to complete his mission of reopening the country.
Depending on how the rest of this arc goes, when Onigashima reaches the Flower Capital, there could very well be a situation where the people of Wano, seeing Yamato in his Makami form, recognize him as a symbol of protection and salvation from Kaido and Orochi, finally making him "Oden" at last. With the help of Momonosuke and the Scabbards and the faith of the people, Yamato could bring Wano into a new era.
