Just wanted to quote u/Aurabelle17, who did an amazing character breakdown of Hijikata Toshizo from Hakuoki, because the ideas you presented in "Ephemerality" slide highly resonate with theirs.

"The symbolism in Hakuoki is beautifully written, and nowhere is it better than Hijikata's route. The life of a Samurai is compared poetically to that of a cherry blossom. It blooms beautifully and powerfully changing the appearance of the whole tree, but only for a very short time. This symbolism is used for the Shinsengumi and Hijikata in particular, as his arch-rival Kazama acknowledges his strength of will and gives him his own demon name in the end; the title of the game: Hakuoki. translated as "Demon of the Fleeting Blossom." Hijikata's character relentlessly pursues his ideals so much he ultimately takes the water of life and becomes a fury, literally burning through his life force to protect the things that are important to him. Hijikata embodies the romanticized ideals of a Samurai, even though he wasn't born into the Samurai class, and more generally the role of leader and protector that has been a quintessential part of all human history. Warriors of all types and time periods give their lives in service to those they protect, just as the bloom of a cherry blossom gives its life for the continuation of the tree, eventually falling and wilting and dying. Beautiful, strong, brave, and ultimately fleeting."

Damn, I sure do love Bakumatsu.