Tokugawa Ieyasu knew that it would not be easy for the Satake clan to change from neutral to favoring him, so in order not to delay time, he did not dispute with Satake Yoshishige over whether to send troops, but instead promised the Satake family when he passed through Mito Castle that once he defeated Hideho, he would reward him with Shimoso-ichikuni. In doing so, Tokugawa Ieyasu did this, in addition to stabilizing the Satake clan, mainly hoping that the Satake family would allow a steady stream of supplies from Edo to reach Aizu through the Mito streets.

Sure enough, after receiving Tokugawa Ieyasu's promise, the forces supporting the Tokugawa clan in the family were more advantageous, and Satake Yoshinobu's neutrality policy was supported by no one except for a few newly promoted retainers, and Satake Yoshishige regained power in the family and sent Satake Yoshinobu to Ota Castle to avoid influencing the central decision-making.

As a result of the Satake clan's compromise, Iwaki Sadataka was forced to open the castle and allow the Tokugawa army to cross the border. In this way, with almost no conflict, the 75,000-strong army led by Tokugawa Ieyasu successfully arrived at Miharu Castle southeast of Nihonmatsu Castle on April 19, and the lord of Nihonmatsu Castle, Tadashi Shimojo, came to meet him in person, and Tokugawa Ieyasu learned from him that just three days earlier, Hideho's crusading army had crossed the Agagawa River into the Aizu Basin, believing that the attack on Wakamatsu Castle had been launched at this time, and hoped that the Tokugawa army would leave for support as soon as possible.

Tokugawa Ieyasu saw that the army was tired and wanted to rest for two days, but considering that Wakamatsu Castle was a flat castle, it was difficult to hold on, so he had no choice but to set off immediately after a half-day rest and march along the streets of Iwaki towards Wakamatsu Castle.

As early as April 17, the Toyotomi army arrived in the area of Fukusenji Temple in the southwest of Aizu, and two miles north was the Yukawa, although the Yukawa was not wide, but it could also play a certain protective role, because after crossing the Yugawa, it would arrive at the Honmaru Gokencho, so the Uesugi family's defensive formation was spread out from the north bank of the Yugawa.

First of all, I would like to introduce the specific structure of Wakamatsu Castle, which is surrounded by Mizuho, and there are bridges to the east, west, and north to Ninomaru, Nishiidemaru, and Kitademaru, and these three bridges divide Mizuho into three parts. The south is called Wuxuan Dinghao, the northeast is Sanqihao, and the northwest is Triangle Hao; The three sub-pills are all based on the Honmaru Mizuho, and the outer maru is dug around it, that is, each is surrounded by water on all sides, and if you want to enter the main pill, you must break any of the three sub-pills, of which the most heavily defended Otemen is located in the West Exit Maru, and the chasing hand gate is located in the North Exit Maru, but the Mizuhiro is wider. The east gate is located in Ninomaru. But there is an ambush in Ninomaru. It can hide a large number of troops, but it is also difficult to capture. Therefore, Hideho's original idea was to attack the south of the city directly, that is, a section without the protection of the pills. As long as the peripheral army is defeated, it can go directly to Wuxuan Ding, use the earth bag to fill Shuihao, and then attack the city, which consumes much less troops than attacking Fenmaru. Of course, the Uesugi family would not have known this, so they deployed 12,000 troops outside the castle to defend the Yukawa defense line to the death.

In the Nishiidemaru South Gate, it is also called the "Inner Gate" near the Jonan Village. There were 1,000 troops under the command of Yamaura Keikoku, the son of Yoshikiyoshi Murakami, and 500 troops under Suda Nagayoshi were stationed in another flat mountain villa; Ikega, southwest of the south gate of Ninomaru, was garrisoned with 1,000 troops of Yasuda Nomoto, and Ikebo was backed by Goxuanding, which was a stronghold closest to Honmaru; The Tsuruhara Plateau, two miles southeast of the South Gate, is a slight plateau near Wakamatsu. On the hill there were 1,000 men of Oishi Tsunagen stationed as a barrier to the western army; Next are the three positions adjacent to Yukawa, which are located between the inner gate and the south gate, and are called Minamimachi, Kitagawahara, and Inomata Village, respectively, and the south town to the west is home to 1,000 Kurokawa Yumi and 1,500 Suwon kinken; Kitagawa Hara in the central part was the most important position, with 2,000 Haruyen Tada, 2,000 Maeda Keiji, 1,000 Nakajo Mimori, and 1,000 Oguni Minori, accounting for half of the forces outside the castle. In charge of the defense of the eastern village of Inomata were 2,000 people from Shida Yoshihide and 500 people from Shimoyoshitada, who had been evacuated from Nanzhuang. Although it was a three-sided defense, to put it simply, the first line of defense of Wakamatsu Castle was the first line of defense of Minamimachi, Kitagawara, and Inomata, and the line of Hirayama, Ikebo, and Tsuruhara in the south of the castle was Wakamatsu's second line of defense.

In Wakamatsu Castle, Uesugi Keikatsu, as the commander-in-chief, led 4,000 men to take charge of Honmaru, Naoe Kanesu's 3,000 men hid in Ninomaru's ambush Guozhong, and Ninomaru's defense was handed over to Kanya Ketsugu's 2,000 men; The west out of Marumizuhao is wider, and the inner gate is guarded by two armies, so there are only 2,000 people in the city who are guarded by the light of the color department; Kitademaru was the least threatened, so there were only 2,000 men, and Nakajo Mitsumori was in charge of guarding it. To sum up, the small Wakamatsu Castle concentrated a huge army of 26,500 people, and Uesugi Keikatsu was desperate to hold out until the moment of Tokugawa Ieyasu's arrival.

Twenty-six thousand people had already crowded northern Sichuan and Wakamatsu Castle, but there was not enough space for Hideho, who had poured out of the nest. After arriving at Yugawa on 17 April, the 140,000-strong army immediately deployed on both sides of Aizunishi Street, with Kimura, Omoomachi, Utagawa-so, and Sugawara Shrine near Yukawa as offensive positions, Kohiyama and Furukawa Shrine as the right flank, Kobayashi Village as the left flank, Fukusenji Temple as the main camp of Hideho, and Jokeiji Temple in the south of the temple as the main army.

Among them, Kimura garrisoned 6,000 Kyogoku Takaji, Otani Yoshitsugu 3,000, Shinjo Naori, and Yamazaki Imori 1,800, totaling 1,800; Omomachi has 3,000 Satake Guna (led by the old Makabe clan), Fukushima Masanori 9,000, Kuroda Nagamasa 5,500, and Hosokawa Tadashi 3,000, totaling 2,500; Utagawaso has 6,000 of the four regiments, 5,000 of Wasuka Housekee, 5,000 Ichikoma 5,000, 5,000 Kato Yoshiaki, and 2,000 of Wakisaka Yasuji, totaling 23,000; Sugawara Shrine has Tanaka Yoshimasa 3,000, Hineno Hiroshi 600, Kobayakawa Hideaki 13,000, and Shima Kiyoko 5,000, totaling 21,600; In Utagawa-so and Tenjinso, south of Sugawara Shrine, there are 5,000 Fukushima Takayoshi and 2,000 Shimono of Nakayama Asanobu, a total of 7,000; In the westernmost village of Kobayashi, there are 3,000 Yamato, 4,000 Minon, and 900 Ikeda Nagayoshi, totaling 7,900; Kohiyama has 4,000 Yuki Hideyasu, Mori Hidemoto 8,000, and Yoshikawa Hiroke 3,000, a total of 15,000; Furukawa Shrine has 1,500 Shimazu Yoshihiro of the Kyushu Legion, 4,000 Yukinaga Konishi, 2,000 Mori Katsunobu, 2,000 Nakagawa Hidenari and 3,000 Aoki Toshiki, for a total of 12,500; Fukusenji Temple, where Hidebo's main camp was located, had 15,000 troops directly under Hideho, 5,000 Fujido Takatora, and a small number of troops carried by the daimyo of Nishimino, Shinano, and Hida, about 1,400, totaling 21,400; The southernmost Jokeiji Temple is home to 4,000 Nasu Shikichi, 600 Kuchigi Mototsuna, Hojo Clan's 600, and Akaza Yoshike 4,000, totaling 8,200. In this way, Hideho's total strength this time reached 146,000 men, more than five times that of the Uesugi army, and it was no surprise that he would definitely be able to take Wakamatsu Castle.