This comparison will relay many key elements of Future Boy Conan's plot, but don't take it as a replacement for watching the series, if you haven't.
In Episode 1, "Remnant Island", Lana, the Heroine, is seen speaking to a bird (named Teki), while the rest of the flock fly around her. When Conan, the Boy, questions her about it, she says "I can tell what they're thinking." When she does, she uses the Japanese term 'kokoro' (心) which can be used to mean mind, heart, and spirit.
She continues to commune with the birds throughout the series, as her power gains more focus and plot significance.
In Episode 6, "Dyce's Rebellion", during Lepka's interrogation of Conan and Lana he says:
"I'm well aware that both you and the doctor (Lana's Grandfather) are telepathic. Now call him. He'll be quick to answer [...] Much like your avian friends do."
In Episode 7, "Chase", Conan tries desperately to swim aboard the Barracuda while his arms and legs are restrained by cuffs. When he calls Lana's name in desperation, she hears it clearly, despite him being fully submerged and clinging to the base of the ship.
Lana: "Conan... Conan's calling."
Jimsy: "No way... He's back in Industria."
Lana: "Conan's calling. I can hear his voice."
In Episode 8, "Escape", a brief telepathic conversation seems to occur between Lana and Conan while they are underwater.
Conan: [Lana, turn back!]
Lana: [Conan, you have to survive. Please! You must!]
It initially seems like a set of one-sided thoughts that only the audience hears, but the two later acknowledge the interaction.
Conan: "I heard your voice back there, even while we were underwater."
Lana: "I heard yours, too."
Conan: "Strange, huh?"
Lana: "Our hearts (心) called out to one another."
Conan: "Like the way you talk with Teki?"
Lana: "Mm."
In Episode 19, "Giant Tsunami", Lana speaks to Conan from a great distance away to warn him of the coming disaster.
Before she says anything more than his name, he already develops a bad feeling, seemingly based on her emotional state.
Lana: [Conan.]
---
Conan: "Mr. Gull, let's come back later. There's just something wrong."
Mr. Gull: "Like what? The ship just tipped because the tide went out."
Conan: "That's not it! Something's been off since a little while ago. My heart's been pounding."
Lana: [Conan! Conan, look at the ocean!]
I'm elaborating on this plot development because I think this mechanic of Lana and Conan's relationship laid the groundwork for a small mechanic found within e-koʊ: The use of the R1 Button while yoruda is away.
When I first made this video, I had yet to watch Future Boy Conan.
After doing so, it felt like I finally had the means to convey what was happening here.
In my video, I certainly made it out to be a tightly defined system with a set of rules. Rules that we could draw out and define from in-game evidence. (After all, I tested it through the medium of a video game, which is a set of rules, in essence.)
But my suggested ruleset of e-koʊ has a sixth sense for Light Magic' was very restrictive compared to the supernatural bond expressed in Future Boy Conan. I pointed out as much in the video itself when I mentioned that e-koʊ doesn't lock onto other obvious Light Magic conduits before the game's turning point. The theory didn't entirely add up. And if the strict ruleset wasn't clicking, then looser rules may be the more fitting reality.
While Ueda could not sacrifice the lack of communication between e-koʊ and yoruda, (and thus did not let them speak telepathically as Conan and Lana do) he did allow e-koʊ to know things he shouldn't, such as her distant location, and when she is in danger.
And that reflects the way Lana knew Conan wasn't "back in Industria" during the events of Episode 7 and 8, because she heard his voice. As well as how Conan experienced some of Lana's stress in his own heart before she managed to explain herself telepathically.
In Future Boy Conan, telepathy helps display the bond between Boy and Heroine, by providing information about the other half of the pair that no one else could reasonably know. I think that's what the 'ESP' I described in e-koʊ is as well. That's why the R1 button expresses itself as it does when yoruda is distant.
Their hearts call out to each other.
But what then of The Queen's Sword?
It's the sole reason I made the more mechanical claim of 'Light Magic Sense' because it doesn't fit this framework.
If e-koʊ is bonded to yoruda, why does he sense the sword in the final boss fight? This inanimate object with no heart and no emotional bond?
The only explanation I could offer that was approaching this was "Perhaps Yorda's soul exited her stone body and joined Ico in the throne room, guiding his senses to the blade when he called?". Though I liked this idea, I was dismissive of it, because it lacked in-game evidence.
Now, I think I believe it more than any other theory.
Because, in Future Boy Conan, Lana uses her power during the series finale in a very interesting way. Conan is lost at sea, and is likely to die of starvation or thirst if not found soon. Lana is distressed, thinking she's powerless. But her grandfather, Dr. Lao, gives her encouragement.
Dr. Lao: "Lana. You can't hear Conan's voice, can you?"
Lana: "I can't... What should I do, Grandfather? I just don't know! I keep trying but it isn't working!"
Dr. Lao: "Lana. You've always held yourself back because you were worried about me, right? But you don't have to anymore. You've done more than enough to shoulder my heavy burdens. Now then, Lana. Go ahead and fly."
Lana: "Fly?"
Dr. Lao: "Yes, fly. If you think only of Conan in your heart, you can fly."
What follows shortly after is a sequence where Lana reaches out with her mind and has an out-of-body experience. She sees through the eyes of her avian friend, Teki. She becomes distant from her body, still standing on the ship, as her soul, her heart, and her mind, are on the breeze with the birds.
With this scene in mind, given how much of Ico, Shadow of the Colossus, and The Last Guardian feel (even lightly) touched by this series, I find it harder to doubt the idea that yoruda could've had a similar out-of-body experience. Even without audio-visual indication of her presence, I find it plausible that her soul could have been in the room, and pointed e-koʊ to The Queen's Sword.