This is an extremely crappy Ova with one of the worst, nonsensical plots I have seen out of all the trash retro Ovas out there.
In between the poorly elaborated apocalyptic plans of the bad guys coming out of nowhere, Riki's brother going from 'don't kill muh brother; ANGERY' to 'Imma destroy all of Japan' within 10 minutes and Riki Oh getting mortally wounded only to fight as if nothing had happened in the very next scene, this anime is like Evangelion in how it chucks in random religious symbols in the hopes that the viewer would over interpret it as a sign of 'intelligence'. However,
even Evangelion manages to have a somewhat coherent plot, Riki Oh's is just shit flinging that hopes it sticks.
Of course any genre savy viewer knows that you don't watch this sort of garbage for characters, plot or anything that you know, makes an anime good.
You watch it for the hilariously cheesy gorefests.
In this regard, Riki Oh truly delivers; at least for the first half. Disappointingly, the gore in the first 15 minute so completely overshadows anything else that happens later.
Art is more akin to a mid 80s Tv show than a 1990s production. It is rather crappy for its time and is absolute garbage by today's standards.
Similarily the music is more akin to mid 80s Nwobhm/ heavy metal. Not a good thing in this case as it is cheesy even for its time and is absolute garbage by Nwobhm standards.
Overall, the only reason you should watch this super trashy Ova is for the gore in the first half, if the gore were better paced and spread out in the anime, there is no doubt that some of these scenes would attain the notoriety on the level of such classics as Angel Cop.