"Donten ni Warau Gaiden: Ōka, Tenbō no Kakehashi" is a three-part anime OVA series that serves as a prequel to the main "Donten ni Warau" storyline, exploring the events and relationships that shaped the characters before the original series. Set in the Meiji era of Japan, the story revolves around the Kumo family, particularly focusing on the eldest brother, Tenka Kumo, and his younger siblings, Soramaru and Chutaro. The Kumo brothers are part of a lineage tasked with sealing away the Orochi, a legendary serpent that threatens the nation. However, their mission is complicated by political intrigue, personal struggles, and the emergence of a mysterious organization known as the Yamainu.

The narrative delves into Tenka's role as the head of the Kumo family and his internal conflict between his duty to protect Japan and his desire to shield his brothers from the dangers of their inherited responsibility. Soramaru, the middle brother, grapples with feelings of inadequacy and a longing to prove himself, while Chutaro, the youngest, remains largely unaware of the family's burdens. The story also introduces key figures such as Abe no Hirari, a skilled swordswoman with ties to the Yamainu, and Shirasu Kinjo, a former samurai who becomes entangled in the Kumo family's affairs.

As the plot unfolds, tensions rise between the Kumo brothers and the Yamainu, who seek to exploit the Orochi's power for their own ends. The series explores themes of loyalty, sacrifice, and the weight of legacy, culminating in a climactic confrontation that tests the bonds between the siblings and their resolve to fulfill their duty. The OVA provides crucial backstory for the main series, shedding light on the motivations and relationships that drive the characters in "Donten ni Warau."