More people are finding Naste sus and that's a good thing. Because I'm pretty sure she has a part in all of this. The current prevailing theory about Ryo being Ramaga (whom I will call Ryomaga henceforth) is probably connected as well. Episode 5 tells us that the original troopers went to seal the youja gate and are now trapped there with no way to be contacted. That makes it easier to believe Ramaga could've gotten hold of Ryo's body and is now using him as a host. In Episode 2, we see a little of the real person underneath Ramaga's armor: blue eyes with a red flower pattern on the pupil. Ryo has blue eyes, so the red flower could be a mark of possession. What I'll share next is my own personal theory about the situation. This is assuming the OVAs are canon. Here's how I think it went down:
LONG TEXT AHEAD FOR MY THEORY
5 years ago, the youja gate opened and the 1st generation troopers + Naste (maybe Jun too) went to seal it back. They get there, but are met by Ramaga and the Ten Braves. They then fight but are defeated due to having grown weaker with age, as well as being overpowered. Just as the youja are about to kill everyone, Naste begs them to stop and proposes a deal: spare their lives and don't invade the human world yet in exchange for whatever Ramaga wants— she will get it for him within 5 years. Ramaga considers and agrees: he'll let them live if Naste helps him achieve his goal of obtaining the last of the 3 treasures (he has the Jewel of Conquest & Sword of Domination already), and that's the "ultimate" armor (similar to Kikoutei, but not the same since it was destroyed).
To achieve this, Ramaga gives Naste the Hasha no Magatama & Seiha no Tsurugi to aid in her search for potential bearers of the 5 virtues, in order to awaken new armors so he can combine them to become the ultimate armor. Naste says ok, and is about to get the others to leave until Ramaga reveals one caveat: he will use Ryo's body and keep the other troopers hostage until she can give him what he wants. Once 5 years pass, Ramaga will return to take back what is his. Naste sadly has no choice but to agree and starts putting her plan into motion.
She establishes the DST and gets government funding, keeping her deal with Ramaga a secret (otherwise they would never allow it), and recruiting troopers for Ramaga's plan using the magatama. In the meantime, Naste tries other ways to contact Ryo and co.; if successful, she may not have to go through with her promise. Unfortunately, the last expedition to youjakai under Ryusei & Shion went badly, and time passes by quickly to the present day. It is now 5 years later and Ramaga has returned to remind Naste of her promise. While he was planning to possess Gai once he turns 15, he also had another idea to gain more power which was part of his deal with Naste.
Ramaga will send Gai out to the human world to be the bearer of the fire armor (which is now Shakunetsu). He had previously informed Naste of this which is why she so easily accepted him into the DST. Once Gai is human and becomes a Samurai Trooper, he can wear Shakunetsu and later the ultimate armor once all 5 are assembled. When Gai defeats the Ten Braves, he will also absorb them, gaining their abilities, and become an extremely powerful host. Ramaga can then possess him and establish himself as the greatest youja emperor, challenging anyone standing in his way.
*Whew* Ok, that was a lot of speculating. Does it cover all the plot holes and possibilities comprehensively? No, I'm sure I missed out a lot of things to come up with this theory. This is also assuming the OVAs are canon. If they aren't, well... maybe some of it could fit. Moreover, I don't know how Gai is connected to Ramaga & Ryo, or where the Ten braves come from. For now tho, it's a rough idea of my theory given what we currently know of the story.
