Ryo

Both shows are set at the end of the Edo (Tokugawa Shoganate) era, 1860s.Both shows feature real world samurai Ryoma Sakamoto and give homage to his ideas. Ryo is a one shot OVA focusing on Ryoma as a person. Hidamari no Ki is historical drama and Ryoma is one of several samurai based on real world entities involved with politics at the end shogunate era. 

Both are homages to famous liberal and progressive samurai Ryōma Sakamoto, a political activist during the late Meiji Period. In both anime, a fictional relation between Sakamoto and a young boy whom he mentors is shown. In Ryo, this is the full plot, in Haguregumo it is just one arc of a character in a more complex story. Ryo is far more serious and historical, while Haguregumo feels more like a nod from an admirer without intended historical accuracy. However, both anime show the assassination of Sakamoto in a Kyoto pub in detail. 

Both talk about orphans during Japan's Bakumatsu era. In Ryo, the titular character serves the revolutionary Sakamoto Ryōma, while in Peace Maker Kurogane, Tetsunosuke, serves in the Shinsengumi. 

Set in the same chaotic time period of Bakumatsu. Both of them have very serious tones, involving bloodshed and only have the mildest of comedies. Ryoma and Kenshin both have loved ones whom they ultimately cannot be together forever due to circumstances. And finally, death is the central theme for between these two.  

This reminded me a lot to RK, its about a boy living in the Meiji era and that sees the horrors of the war 

Historical anime taking place in Edo Japan. Akizuki from Bakumatsu served as Ryoma Sakamoto's bodyguard. Members of the Shinsengumi are here too. 

If you like Ryo and interested in that historical period then try Shura no Toki. The 3d arc of SnT describes life and death of Sakamoto Ryoma more clearly