"Destiny" 「相思相殺 Sōshi sōsatsu」 is the first episode of Basilisk.
At Sunpu Castle, Yashamaru of Iga Tsubagakure and Shōgen Kazamachi of Kōga Manjidani are engaged in a ninpō battle. Their respective leaders, Ogen and Danjō Kōga, watch the battle from a distance, along with the shogun Ieyasu Tokugawa and his generals, Masahiro Hattori and Munenori Yagyū. Yashamaru seemingly kills Shōgen with his ninpō, Kokujō. However, Shōgen survives the attack using his flexible physiology. He uses his ninpō, Phlegm, to bind Yashamaru's hands. Unable to use his ninpō, Yashamaru resorts to using the Kokojō bound to his legs to break free from the phlegm. The two continue the battle atop the Sunpu Castle, attacking the other with neither of the two being able to land a successful blow. Witnessing the ferocity of the ninpō battle himself, Masahiro realizes why his ancestor had implemented the Anti-War Pact between the Iga and the Kōga, but wonders why Ieyasu wished to witness the battle.
A while earlier, Ieyasu had visited Tenkai Nankōbō over his concerns regarding the selection of the next shogun. Tenkai suggested using ninjas to decide between Takechiyo Tokugawa and Kunichiyo Tokugawa. He devised the Kōga Iga War as a method to decide the next shogun without costing the Tokugawa any samurai. Iga Tsubagakure would represent Takechiyo in the war, while Kōga Manjidani would represent Kunichiyo and the side with the final survivor would win.
Having seen enough, Ieyasu orders the battle to be halted before Yashamaru and Shoōgen could deal a fatal blow to each other. He puts forth his plan of picking the next shogun before the two leaders, who readily accept the offer, explaining that the rivalry between the two clans was reason enough. Masahiro revokes the Anti-War Pact on Ieyasu's orders. With the peace treaty now broken, Ieyasu hands a scroll each to both Koōga and Ogen and asks them to write the names of ten of their ninjas who would participate in the war. After declaring the conditions of the war, Ieyasu promises one thousand years of glory to the winner of the war.
After leaving Sunpu, Ogen and Danjō hand their scrolls to Yashamaru and Shoōgen, respectively, and order them to report to their respective villages. As Yashamaru leaves, Danjō slyly steals the scroll from him. Now alone, Ogen and Danjō reminisce about the past, back to the time when the two were in love with each other. They often met each other in secret, due to their clans being bitter enemies for centuries. They had hoped their clans would reconcile with the Anti-War Pact. While returning to Iga Tsubagakure from one such tryst, Ogen and Danjō found themselves amidst an invasion of Tsubagakure led by Nobunaga Oda. They rushed to the village and discovered Oda samurai brutally murdering Iga civilians that Danjō ends up killing. After rushing back to Ogen's home, they found her grandfather, fatally wounded, surrounded by Iga ninjas and Masanari Hattori. Hattori urged them to escape the place immediately along with the other survivors before more of the Oda arrived, including Nobunaga. Ogen initially refused to escape, but Danjō convinced her and the two promptly left the place along with a few Iga ninjas. As they were escaping, the group was attacked by Renbu Kasumi and the Kōga, implying that the Kōga was heavily involved in the invasion too. Although Danjō denied the allegations of any involvement, Ogen felt deceived. She ended her relationship with him and attacked him.
Ogen and Danjō discuss the ninjas whose names they had put on their scrolls, when Danjō attacks Ogen, spitting a senbon into her throat. He takes out the scroll he had stolen from Yashamaru and strikes out Ogen's name from it using his own blood. Ogen struggles to speak and Danjō throws another senbon into her mouth, bidding her farewell. Believing her to be dead, he is distracted by a hawk when Ogen pulls out the senbon from mouth and stabs him through the chest with it, killing him immediately. Using Danjō's blood, Ogen strikes out his name from the scroll and falls on top of his corpse as she mourns his death, while their bodies drift into the river. The hawk then picks up the scroll and flies away.