So I was browsing this Kaitou Ace shrine the other day when something caught my eye. There's an article listed on the side bar that appears to have never been written but the title is interesting:
"fifth shitennou? dark heir"

Now, this lady seems to know her stuff so I don't think the title is proposing that he's a long lost member of the original Shitennou as Mamoru's entourage. His backstory as a Venusian makes that completely clear.

But there has always been an unanswered question as to whether and how Danburite/Ace of the Dark Kingdom in the 20th century interacted with the Four Heavenly Kings. I find it an especially fascinating question given he seems to know about Venus' attraction to Kunzite in their past lives and could have served directly under him at the time. But in Beryl's new rule, given the number of underlings he has, it seems to me like Danburite was probably on the same level hierarchically speaking as Kunzite.  

What do you guys think? Did Danburite and the Shitennou ever meet? And since he was from the lower ranks of the interplanetary(?) army used during the Silver Millennium, so probably unknown to Beryl, why was he reincarnated by her in the first place? Are there any hints at all about these things?? I mean, it has been a few years since I last reread it XD.

So many questions!

I always thought that Queen Serenity reincarnated everyone to be reborn on Earth, so in that case it's little wonder that Adonis was also reborn. As for how he came into the service of Beryl, I feel like Beryl sought of people who were reborn who had some amount of inherent power. Adonis, even though he was a soldier of Venus who served under Kunzite, might've had some level of magical power that got him into the general's service to begin with. Beryl might've found people like him, brainwashed/manipulated them so they would work for her. The irony of course, is that she failed to find the most powerful reincarnated beings from that era, namely, Usagi and Mamoru. Perhaps Adonis and the Shitennou had already began to awaken (I think in the manga Kunzite(?) mentioned they had began to recall their pasts when Beryl found them?), and their awakening power enabled Beryl to locate them, but not the prince and princess she really wanted to find.

Disclaimed: this is all just head!canon I thought up on the spot. I'm not sure I can develop it any further than what I've written here.

What about Fluorite? She was Danburite's subordinate as far as we know, but she also had a mineral name and appears as human as him or the Shitennou. (I could believe that the likes of Pandora, Petite Pandora, the Dark Boys, WanWan, etc are all Youmas, though, like Morga.)

If Danburite worked for Kunzite, then that means people from Venus were working for the people of Earth (as Kunzite is from Earth I think). In that case, Danburite might be an immigrant to Earth, or they might have some sort of deal with the other planets the way the moon does (like why Princess Serenity's guardians came from other planets).

However, are we sure Danburite wasn't actually a subordinate of Venus who simply never spoke up to interact with her because of his low station or something? I'm unclear on all this myself.

We also don't know how early Beryl reawakened. Did she find the Dark Kingdom before Danburite and Fluorite set up their 'Dark Agency', or afterwards? Is the 'Dark Agency' subordinate to Queen Beryl and the Dark Kingdom? Also, the Agency seems to have operations spread out in places like Greece (wouldn't that be closer to Kunzite's territory, if the Shitennou were each overseeing a quarter of the Earth) in addition to the main bulk we see in Japan. In any case, I'm pretty sure they said Danburite was the leader of the Dark Agency.

In the '90s anime continuity, I can't find a single reference to life on other planets or orbital castles or any of that, so there I'm inclined to think that Sailor Venus and the other Inners are all from the Moon, and that the only inhabited places in the Solar System (until Nemesis in the future) are the Earth and the Moon. Here, I think that in the era of Silver Millennium and the Golden Kingdom, perhaps the other planets were just as hostile to life as they are in real life present day (Venus is hellish IRL). We don't know if Danburite existed in this timeline or not, but if he did he would probably be from Earth in that timeline.

Then again, in the '90s anime even things like age seem to vary (Asanuma is a friend of Mamoru's when Mamoru himself is a bit older and in college, and Asanuma looks like he might be college age himself, in Sailor Stars...) so I think he could really plug in anywhere for that timeline, but I could easily see him having some involvement in the Golden Kingdom, and in the unseen adventures of Sailor V. (Also, if what I heard about a Sailor V OVA being planned in the 90s but cancelled is true, Danburite likely would've appeared in that.)