In 1573, while laying siege to Tokugawa's fortress at Noda, Shingen was shot by a sniper when he moved his position forward to listen to a defender play his flute. A few days later, because of complications, he would die. He made his vassals promise to keep his death a secret for two years. It was not until April of 1575 that his death was made known to the public. For his son, Katsuyori, his father's funeral not only put closure on the secret, but also his appointment as the next leader of the Takeda.

Shortly after Katsuyori's appointment, Tokugawa Ieyasu challenged him by making one of Takeda's former allies, Okudaira Sadamasa, commander of Nagashino Castle. Nagashino had strategic importance. It guarded the entrance to Mikawa and Totomi. The castle, situated where the Takigawa, Onogawa, and Toyokawa rivers met, was a strong defensive position.

In 1575 Oga Yasahiro, a financial official to the Tokugawa, turned traitor and offered to open Ozaki Castle to a Takeda advance. Ozaki, the capital of Mikawa, was important to the Tokugawa. Its capture would assure the downfall of the clan, and for this reason Ieyasu had appointed his son, Nobuyasu, to command it.

Meanwhile in Kai, Katsuyori decided to take Oga up on his offer. He set out of his capital at the head of 15,000 men, headed for Okazaki. While en route, he found that Oga's scheme had been discovered. If Katsuyori withdrew now he would lose face. Nagashino Castle was in range of his army. Against his vassals' arguments, he marched his army to take possession of it.

Nagashino was commanded by Okudaira, who had 500 men. He was determined to get back at Katsuyori for the execution of his wife and brother. He and his troops put up a great defense, which the Takeda could not penetrate. Katsuyori decided to avoid any further assaults. Palisades were placed and the rivers blocked by ropes, then the Takeda sat back for a long siege.

A defender in the garrison, Torii Suneemon, volunteered to take a message to Ieyasu. At midnight on June 22, he slipped out of the castle, swam the river, and made his way past the siege lines. He then proceeded to Ieyasu. When Nobunaga and Ieyasu heard the news they immediately acted. They knew the castle could hold out for only five days at most. The next day they marched out of Okazaki with 32,000 men. Meanwhile, Torii had decided to go back to the castle and tell them the news. However, a trap awaited him. He was caught and strung up on a cross, and told to tell the garrison that all hope was gone; the penalty for not doing so would be death. Instead he called out to the garrison to hold their ground; help was on the way. He was quickly silenced.

Katsuyori held a council of war with his top generals. They urged him to withdraw, but he would not. Then they argued for a fierce assault on the castle in order to take it and prepare it for siege, again, Katsuyori refused. Like Ieyasu at Mikata, Katsuyori was determined to fight them in the open, where the mighty Takeda cavalry could be best used to destroy the enemy.

The Oda allied army arrived on the June 21. That night Sakai Tadatsugu led 3,000 men on a raid of the Takeda camp, managing to kill Katsuyori's uncle, Nobuzane. Meanwhile, Oda had his men prepare positions for the coming battle. He knew the strength of the Takeda was their cavalry. He would render them useless by a palisade stretched along the Rengogawa, while the rest of the army defended high ground behind it.

The morning of the battle, Oda made final preparations of his line. He placed 4,000 under Oda Nobutada about a mile to the rear, while 3,000 maintained pressure on the Takeda siege force. Okubo Tadayo was placed with his troops out in front of the line as bait, along with detachments of Sakuma Nobumori. The rest of the troops positioned behind the Rengogawa around Danjohyama. For the first time, Nobunaga was entrusting victory to his Ashigaru with a front line position. He detached 3,000 arquebusiers under Honda Tadakatsu, Maeda Toshiie, and Sase Narimasa, placing them behind the palisade. They had orders to fire at short range, and to shoot the horses first.

Katsuyori was busy arranging his forces. Maintaining the siege was 2,300 troops. The rest, some 12,700 men, took positions in three divisions on high ground opposite Danjohyama; 3,000 under Baba Nobuharu, 3,500 under Naito Masatoyo, and 3,700 under Yamagata Masakage. The rest positioned in the center with Katsuyori. At 5:00 A.M. the Takeda trumpets sounded. Katsuyori sent in the first wave of men into the attack. The battle of Nagashino had begun.

The Takeda cavalry charged down the hillside and up the fields towards the Rengogawa, which slowed their momentum. Picking up speed again, the cavalry continued. At 50 meters from the palisade a volley blasted their ranks, but they continued. Then a second and third volley tore into them, killing many and disordering the advance. The Oda allied forces fell upon them. On the left flank, Yamagata was lured into attacking Okubo, preventing him from supporting the center. On the right, Baba too, was lured into attacking the Sakuma, preventing him from supporting the center. Sakuma's troops faked a retreat, allowing Baba's men to get into volley range; they were shot up. Shibata and Hideyoshi fell upon them, driving them back. Katsuyori ordered in all his reserves; again they were shot up, then cut up by the Oda. Back in Nagashino, Okudaira led a sortie out of the castle, hitting the Takeda in the rear. By 12 noon the battle was over.

A tremendous price had been paid for Katsuyori's refusal to withdraw. About 10,000 of his clansmen were killed. Out of 97 Samurai leaders, 54 were killed, including seven of Shingen's original 24 generals; Baba Nobuharu, Hara Masatane, Sanada Nobutsuna and his brother Masateru, Yamagata Masakage, Saigusa Moritomo, Tsuchiya Masatsugu, and Naito Masatoyo. Obata Masamori would die later from a wound received. The Oda allied side lost 6,000 men. The battle had been decisive. From now on the Takeda would only be a shadow of its former self. Eventually the clan would be destroyed in 1582.