The best way to see "Rurouni Kenshin" is currently via Hulu. The show's first season is available on the animation streaming platforms Funimation Now and Crunchyroll, as well as VRV, all of which fall under the same parent company umbrella. It's also available on Hulu, all of which carry the entirety of the 28-episode first season.
The second season, however, is only available on Hulu — and to make matters a bit trickier, not all of it is on the streaming platform. Of the 35 episodes that comprise the show's second season, only 13 are available on Hulu, with the rest not currently on any streaming platform. The entirety of the third season's 33 episodes, however, are available on Hulu.
As of the writing of this article, none of the seasons of "Rurouni Kenshin" are available for digital purchase on any platforms. DVDs of the show's three seasons, however, are available on platforms such as Amazon. The movie continuation, as well as the Original Video Animation continuations, are not currently available on any streaming platform. The live-action movies, however, are available on Funimation and Netflix.