This sounds silly, but there is reason to believe that Martha Astor, the protagonist of Oakburn Opus, is the Wendigo from VHS Tales' "The Starving Five". Here are the reasons:

1.While it's not explicitly connected to Oakburn like "The Circles", symbolism links "The Starving Five" to Oakburn Opus.

Examples of the connections:

• The eye close-up motif from "The Starving Five" appears in Part III.

• John Doe takes on a three-part appearance, similar the Wendigo's as he channels Marvpyas at the end of Part II.

• Oakburn as a whole continues the "not investigating missing person's cases as they fear the truth" themes of the Dec. 17 phone call from "Starving Five"

2. According to Part III, Martha Astor is an supernatural and immortal being.

It's implied that Martha is the immortal reincarnation of Martha Ludolf and the fish-like thing in the Sunken City is the immortal Matthaus Ludolf, because the two are associated with those people's runes during the Sunken City scene.

In the 1850s, Martha Ludolf died, and Matthaus sold his soul to Marvpyas in order to grant the two immortality. However, Marvpyas tricked the two, stealing Matthaus's former body to become the Flutist's and locking the transformed Matthaus up in the sunken city. Martha is then cast out into the world with her memory wiped. Matthaus is forced to wait over a century to see his wife again, while Martha is obliviously married to Ethan (and dating someone else, but we'll get to that).

This situation is reflected in the last lines of "Turn Around, Look At Me" (whose first lines were sampled in the video for Martha and Matthaus's meetup):

"Oh, I've been waiting,

But I'll wait forever,

For you, to come to me.

Look at someone who really loves you,

Yeah, loves you.

Turn around, look at me!"

The Wendigo is also immortal in a way very similar to our theorized immortality of Matthaus, being "an exiled spirit, rejected from the domains of the afterlife... preventing it from rotting."

Before I tie it all together the last, most damning piece of evidence:

3. Garry's lover, who became the Wendigo, was a female Astor.

According to the missing posters, Garry, the one who leads them into the wilderness in search of his unnamed missing lover, has the last name of Astor. This means that (assuming they married) his wife was an Astor too.

The only female Astor we know is Martha, who we have already established is supernatural. Garry can't be Martha's son or dating her daughter, as "The Circles" does not mention any children in the Astor house and the house does not have photos of anyone besides Martha hanging on the walls. Garry also can't be Ethan's father, as both parents die and "The Starving Five" does not mention any children, who would have at least had their views on the disappearance compared or contrasted with Garry's.

The most logical relationship between Ethan and Garry is brotherhood, while any way you frame it someone is dating their dead brother's widow.

While we're on the topic of framing, there are three possible timelines you can put together for Martha Astor. They all start the same:

1. 1852s: Martha and Matthaus Ludolf marry.

2. 1897: Town of Oakburn is founded.

3. Martha dies at the hands of Oakburn residents.

4. Matthaus sells his soul to Marvpyas to revive Martha and give them both immortality.

5. Matthaus is trapped in the sunken city and Martha is yeeted into the woods.

6. Early/mid 20th century: the Flutist appears in Oakburn.

Here's where the timelines diverge. It's never explicitly stated which year "Starving Five" takes place, so it could happen either in the 1950s-1970s, before Martha's marriage to Ethan; anytime from 1986-2000, between "Circles" and Part I, or and after the events of Part III.

Here's the "pre-Circles" timeline:

1. 1950s: Martha emerges from the woods (under a different name) and seduces young adult Garry Astor. They marry.

2. Eventually, Martha returns to the woods and becomes the Wendigo. Garry & Friends follow, but are killed.

3. 1970/80s: Martha, as the Wendigo, dies and reverts to her human form, without any memoires of her past.

4. She returns to Ittosiviik, and no one recognizes her. She finds someone who is similar "enough" to Garry: his brother Ethan. They marry.

5. December 1986: Events of "The Circles".

6. In response to the supernatural death of her husband, Martha joins the Ittosviik PD.

7. 1997-2003: Events of Oakburn Opus.

This timeline explains Martha's memory loss and the archaic phone seen in "Starving Five", but it's weird in that fact that Ethan is oblivious to Martha's true age and her past with his family; it also means that Ethan must have been old (while not as old as the immortal Martha) when he married Martha in order to be brother to someone who was 20 in the 1950s.

Here's the "post-Circles" timeline:

1. 1970/80s: Martha emerges from the woods. She may not have memoires of Matthaus and her past.

2. Martha then seduces young adult Ethan Astor. They marry.

3. December 1986: Events of "The Circles". Martha is now single.

4. In response to the supernatural death of her husband, Martha joins the Ittosviik PD.

5. Early 1990s: Martha finds someone who is similar "enough" to Ethan: his brother Garry. They marry/begin a relationship.

6. Martha returns to the woods and becomes the Wendigo. Garry & Friends follow, but are killed.

7. Soon after the events of "Starving Five", Martha, as the Wendigo, dies and reverts to her human form. If she had any, she lost her memoires of her supernatural nature and past.

8. Martha, who as only been missing for a few months, returns. No one thinks much of it.

9. 1997-2003: Events of Oakburn Opus.

This is the timeline I think is the least likely, but it is a possibility. It solves the "knowledge of previous relationships leading to figuring out the immortality" problem buy scrunching the timeline, but it's a little far-fetched for Martha to go missing and no one to care (esp. Martha herself).

Here's the "post-Part III" or "Part IV" timeline:

1. 1970/80s: Martha emerges from the woods. She may not have memoires of Matthaus and her past.

2. Martha then seduces young adult Ethan Astor. They marry.

3. December 1986: Events of "The Circles". Martha is now single.

4. In response to the supernatural death of her husband, Martha joins the Ittosviik PD.

5. 1990s/Early 2000s: Martha finds someone who is similar "enough" to Ethan: his brother Garry. They marry/begin a relationship.

6. 1997-2003: Events of Oakburn Opus.

7. After meeting Matthaus in the Sunken City, something occurs that transforms Martha into the Wendigo.

8. After his wife fails to return from her investigation after a month, Garry Astor hears Martha's "call" and he and his friends follow. They are killed.

9. Martha, due to her quest for the truth, is left permanently the Wendigo.

I think this timeline is the most likely (after "pre-Circles") and would be the easiest to reveal in Part IV. Martha never disappears and returns, so there's nobody to recognize her as immortal. The Wendigo also never dies, (so it's the only timeline that complies with the "Starving Five" opening narration).

Another piece of evidence for the "Part IV" timeline is the fact that John Doe says that Martha's quest will lead to the deaths of "the few living people you care about".

This is both evidence of Martha's immortality ("living") and the fact that Martha is in a relationship that she will destroy, which she does when she becomes the Wendigo.

Anyway, that's my theory!

TL, DR: Martha Astor is the Wendigo from "The Starving Five" because she was revealed to be immortal, and freeze framing on the missing posters in "Starving Five" reveals that Garry's lover (aka the Wendigo) was a female Astor.