Dragon Quest V is sort of a sequel to Dragon Quest IV, which sounds painfully obvious, but really isn’t. The numbers simply refer to release order, not the order in which the games take place; and many of them aren’t related at all. DQ5 apparently had no real relation to 4 at first other than the existence of Zenithia and Nadiria, but I understand some other references were worked in for later releases, like the DS version I played. All three women the protagonist can marry are of Zenithian descent, and hence are presumably descended from the hero of DQ4, the only known person to have a human and a Zenithian as parents. This hero can be either male or female, and if the former, the suggestion seems to be that his partner is his friend Eliza, who herself might be at least part elvish.
If the hero is female, then…well, Eliza can change her shape, so maybe she still could be a parent of the hero’s children. (From what I understand, this was the original intention for Nightcrawler from the X-Men; Mystique was actually his father, due to her shape-shifting ability.) While Bianca’s father is an innkeeper called Whitey and Nera and Debora’s the wealthy Rodrigo Briscoletti, it’s revealed that all three were actually foundlings, and might all be biological siblings. The protagonist’s parents were known in Japanese as Papas and Martha, almost certainly intended as plays on “papa” and “mama.” The English translation calls them Pankraz and Madalena, or Mada for short, keeping the same general idea while making it a little less obvious. “Madalena” is derived from “Magdalene,” as in Jesus’ follower Mary. Although it’s not clear in the Bible itself, Mary Magdalene is traditionally seen as the same as the Mary who has a sister named Martha, who would hence presumably also be from Magdala. And I suppose I should also mention that Superman and Batman both have mothers named Martha, at least in some continuities. Pankraz is the King of Gotha, and Mada one of the keepers of the entrance to Nadiria on Lofty Peak. The Loftinians are also known for taming monsters, a skill the protagonist inherits.
At the beginning of the game, Pankraz suggests Madason as the hero’s name, as he’s literally Mada’s son. The default names for the protagonist’s kids, regardless of which wife he chooses, are Parry and Madchen, keeping the same initial letters as his parents’ names. “Madchen” (well, with an umlaut on the A) is German for “girl,” and “parry” is what the Defend command was called in earlier English DQ translations.
While the Japanese called Papas’ kingdom Granvania, in English it’s Gotha, and there’s another kingdom called Coburg (Reinhart in the Japanese). Saxe-Coburg and Gotha was a German duchy, and also the name of the current British royal family before they changed it to Windsor when being German was no longer cool. In the game, Gotha has a Prince Albert and Coburg a Prince (later King) Harry, the latter starting out as the irresponsible sort the current Prince Harry was often portrayed as in his younger days. That might be a coincidence, as the character was called Henry back in the Japanese Super Famicom release, when the real Prince was only eight years old.
At the time of DQ4, the Zenith Dragon, ruler of Zenithia, is generally beneficent but also aloof, only helping humanity when he deems it absolutely necessary. He seems to have become more interested in humans over the years, perhaps due to boredom, and takes human form (as Dr. Agon in the pun-filled translation) about twenty years prior to the events of 5. He also takes on a much less formal personality, talking a lot like Ned Flanders.
During his time on Earth, monsters remove and throw out the Golden Orb that keeps Zenithia Castle in the air, and crashes into a lake. In the course of the game, you restore it and the Dragon, although he takes human form again after you beat the main boss.
The tower to Zenithia still looks basically the same as it does in 4, and is again located near the center of the map (which shouldn’t really mean anything on a spherical world, but that’s a different topic), but is no longer operational. Otherwise, there aren’t too many similarities between the maps in 4 and 5, although they’re closer to each other than either one is to that of 6.
It’s said that Helmunaptra, the Egyptian-themed desert kingdom where the Zenithian Helm is kept, was founded by one of the hero’s companions from DQ4. Which one isn’t clear, but fans have guessed Meena or Hank Hoffman Jr., the latter of whom founds a town in the desert in the DS remake of 4. I’m not sure whether the reference appears in the original release of 5, but if it does, it’s likely not Hank.
The main villain this time was originally known as Mirudraas, called Mildrath in some fan translations. The official translation changed the name entirely, calling him Grandmaster Nimzo after Aron Nimzowitsch, a Russian-born chess grandmaster. This fits with how many of his minions are named after chess pieces and speak with pseudo-Russian accents. Nimzo’s own dialogue is in a Cyrillic font with Russian letters, although they’re used in the traditional jokey way of, for instance, the letter that looks like a backwards R used in place of the English R, when it’s actually pronounced more like “ya.” His followers make up the Order of Zugzwang, also a chess term, meaning you have to make a bad move. It’s officially led by King Korol, although he turns out to mostly be a figurehead.
I’ve seen it pointed out a few times how similar his name is to King K. Krool, who’s also a crocodile; but this is presumably a coincidence. “Korol” is the Russian name for a chess king, and Queen Ferz and Kon the Knight were also named this way. The two remaining leaders in the cult, Bishop Ladja and Slon the Rook, actually have their names reversed (“ladya” is a rook and “slon” a bishop), my guess for the reason being that Ladja is a more sinister villain, and the name sounds more sinister in English. I think it really just means “boat” in Russian. “Slon” literally means “elephant,” an alternate name for a chess bishop; but none of the Zugzwang members resemble elephants, even though the game does have elephant monsters. Kon the Knight, however, does look like a horse.
In the remake, Nimzo is said to be an inhabitant of Lofty Peak who became its ruler, but still sought more power, and so turned himself into a demon with the Secret of Evolution that Estark and Psaro had used.
A character in Coburg Castle called Darwin the Psarologist (apparently Psaro lent his name to a science) is also studying this secret. There’s a building south of Nimzo’s hideout in Mount Zugzwang that a skeleton says used to be the great dungeon of Nadiria, although it’s since been converted into a gameboard. Is this what remains of Psaro’s castle, or some other place?