This is one of the most abstract releases in Sound Horizon, yet you can pull so many meanings from it. It's truly the Profound Meaning of the Third as mentioned in Hoshi no Kirei na Yoru from the Halloyoru single.

I've been in the process of making a post about how the principles of Lost really do appear anywhere and everywhere in every Horizon, analyzing the similarities and differences of every appearance of water symbolism. I plan on posting it in the theories section of this site, but I'll link to it here, I guess...

Although...with the news of Bastet, I'm not so sure if people will be interested in reading a Lost-centric (but really, how it applies to nearly every release) theory post...

Big thanks to Alchea and Sorau for helping me understand it better. It's one of the toughest Horizons to talk about objectively because of how vague its overarching conflict is. There's also the red spider lily imagery in Hiiro no Hana that is very powerful and plan on analyzing in the future.

Ghostie wrote:

It's one of the toughest Horizons to talk about objectively because of how vague its overarching conflict is.

I feel also that the duality of Observer and Acter is less clear in Lost than it is in most of the others, with only the exception of Chronicle.
In Lost, we clearly have the Observers (is there a synonym for "observe" that starts with E?) in the form of the boy and the girl, but the Acter seems to be absent in most of the songs. There is one in the 2nd track (Koibito, being the person who shot their lover) and the 3rd (Mahoutsukai, the young man who is the focal point of the story), but it gets somewhat vague shortly after that.

Who is the Acter in Ushinawareshi Uta, for instance?

Lost is maybe also the Horizon with the meaning that most escapes me, so I'm full ready to admit may I have no idea what I'm talking about.

I wasn't sure where to post this in the Lost discussion or the theory thread but I think this would largely aim at newbies.

I haven't even really checked out Lost all that much but would make time to listen all of the tracks soon enough, now that the later horizons have been published. I think Ghost Savant (with the help of Sorau) did a good job trying to interpret what Lost could possibly mean with the allusions to Freud's take on the water and womb. What I'm largely trying to say is however, that I think looking several incidents in the later horizons, you would see the theme of what Lost was trying to come across. Lost is best served as a complementary hora. You might not see it as a favorite, but it's still very important to check out.

Ghost already pointed stuff out in sanhora, so I'm going to just list them again BECAUSE WHY NOT AND I'M JEALOUS BECAUSE HE POSTED SO MUCH STUFF THAT MAKES SANHORA SENSE. Some being more literal with the theme of water while others more subtle.
- Roman doesn't directly reference Lost as much, but it still applies with the idea that Hiver forgot who he was and he is reborn every time, only to die in the same cage as Michele. He returns to life but only to suffer once more.
- When Missia dies she is literally rising above the water and then returning from Thanatos to what we could assume, nothingess. She is gone. Elef is pissed after that.
- When Abyss dies, it refers to him going to a near-death state, "the sinking water bottom of consciousness"
- The bottom of the well in Marchen. Mars dies and reborn as a vengeance conductor made of Id and Therese's vengeance. He forgets who is exactly, so he's basically a lost soulm but found his identity in the end, thanks to Elisabeth's message of loving him who he is (Easily one of the best parts in Horizon)

Yes, these are some nice things to point out (and I'm glad you posted it here and not in the water bottom topic). A lot of fans might not realize just how many connections Lost has with other releases. The breadth of this release is often underestimated, and is living proof in my mind that the Horizons aren't exactly standalone "worlds" like some may think. How you interpret those connections is entirely up to you and branches out more into the realm of theories, but that's besides the point. I think it may be Revo's most symbolic and profound release in terms of being almost completely abstract but so meaningful at the same time.