On the whole, although the poems you excerpted are from different authors, and their life characters and achievements are also different, we can see the character characteristics of Japanese martial arts heroes. They pursue the realization and glory of the value of life, and have a firm belief in their hearts. It does not matter whether life is short or not. What is important is the glory of life in this world. But at the same time, influenced by Buddhist thought, there is a breath of life, and life is like a dream. The emotion and realization that everything comes to nothing when you die. Therefore, "The body is like morning dew" contains both the emotion about life and the understanding and insight into the multiplicity of lives. This is the true Bushido of the traditional Japanese martial arts, which is different from the crazy things of the later Japanese militarists. If I insist on saying so, the Japanese devils are not Bushido but beastly. Bushido emphasizes loyalty and justice, not madness and killing.
I have not found the exact information whether Uesugi Kenshin’s poems are death poems. We can learn about Akechi Mitsuhide's "There is no difference between good and evil, and the great road runs through the heart" from his life. Akechi Mitsuhide was originally a powerful local sect and later surrendered to the overlord Oda Nobunaga. However, he later took advantage of Oda Nobunaga's unpreparedness and launched a rebellion and surrounded Oda Nobunaga and his wife who were alone in the temple at the time. Oda Nobunaga and his wife died in the battle, and the Oda clan was defeated. It is known in history as the Incident of Honnoji Temple. Later, Oda Nobunaga's right-hand man Toyotomi Hideyoshi and Tokugawa Ieyasu, another overlord at the time, led their troops to judge, and Akechi Mitsuhide was defeated. This will help you understand this poem. Of course, I don’t know what his so-called “big road” is. He looks like a capricious villain.
Maybe his own "big road" refers to his own dream of domination?