In the original history, Senadina and her companions arrive on an incredibly hostile Mars, as the Honkai reacts to their high technological advancement with dangerous monsters. A lot of her friends are killed, some sabotage them or flee, and they eventually don’t have enough resources to let more than one person stay alive at a time.
So they come up with a plan: They put everyone to sleep in cryopods and if someone wakes up the older one needs to die so they can maximize the survival of the group.
Senadina is the second person to be awake, having to watch the elder of their group starve himself to death so she can have the food supply. She’s diligent in her duties looking after their camp, and uses her time to weave a collective dream to soothe her companions, where nothing went horribly wrong… but one of her friends is about to wake up, so she decides to leave.
(She also observes that her Permanence path powers seem to have mutated on Mars, granting her more control over Honkai energy.)
She has to go through a horror sequence to leave and then nearly dies outside, but Senadina is saved by a sapient Honkai Beast she had named Entropy. Entropy was always strange, a very strong monster but it never attacked them, only attacked itself… Senadina finally learns that Entropy has been squatting her shadow, enamored with her ever since she was given a name, but so so so scared. Entropy was the one telling her to kill her friend to survive and trying to stop her from leaving the safety of their ship, she even infiltrated the dream that Senadina made to bond with her while seeming more palatable. This Entropy is the baby form of Leylah, already utterly obsessed.
Senadina tells her that all that is unnecessary and convinces her to take her to the source of the Honkai, which she calls Endlessness. Vita comments that on Venus it was called the Abyss, and on Earth it was called the Honkai— she’s headed to meet with the Cocoon.
After a total of ten years, including several to reassure Entropy and teach her about humanity, Senadina ascends as an imperfect god to swap reality and dreams. She’s essentially enacting Kevin’s plan from the finale, because she realized the Honkai doesn’t attack dreams, and they’ll be safe at the cost of leaving reality behind. Leylah and Serapeum (the sapient moon of Mars) gain a human form in the dream. All is well for quite a while, and Difeng is founded, but instead of the Honkai now it’s decaying because of the corruption from the Sea of Data.
Vita clarifies that swapping dreams and reality pretty much just created a giant Bubble World in the sea of quanta, which means erosion rules apply to it. Senadina has to spend a lot of effort making sure it doesn’t dissolve, but she gladly takes that over the horrors of reality confronting the Honkai.
Looking for a permanent fix, Senadina attempts to do what Kiana achieved with Finality for many years, but she never succeeds, hence introducing herself as the Cocoon of Unwoven later.
Another important tidbit is that Senadina met with Sa in a timeless dream of the Cocoon while attempting the embrace. They had a chat, and Sa made a bet with her, promising to kill her should she become shackles for humanity… which they both immediately forget because of Cocoon dream nonsense. They were never alive simultaneously, after all.
Eventually, the corruption is too much for Senadina to fix, and Difeng is destroyed. As a last ditch attempt to save Mars, Senadina sacrifices herself and pulls the Serapeum moon down to Mars to fill in the literal holes left by the corruption of the Sea of Data, and leaves Leylah in charge.
Leylah is obviously not cool with that, despite Litost’s attempts to get her to act as a proper god. They rebuild and create new cities across Mars, yada yada, you’ve already seen that part.
Then, later, Leylah uses the Mars system to revive Sena for real. However, Leylah chooses to erase her negative memories to make her happy, and leaves her in a mind-numbing simulation where nothing bad ever happened and nothing ever changes, which is horrible for her mental health.
Eventually Real Senadina dreams of Entropy from the System, which let her escape a bit. She also meets with Kiana, interacts with Entropy in the simulation and connects to her thanks to Sera and so on. By present time, she’s trying to die to thwart Leylah’s obsession with her.
So Vita is meeting with the real Senadina, albeit a fragment of her.
We also learn a bit more about the Senadina that Entropy met first and had impossible memories of: she’s an alternate, impossible Senadina created by her daydreams of happiness, a Sena who is a peer with no big responsibilities of godhood, a Sena who never raised Leylah, someone who is free to be happy with her as equals and go on adventures. A carefree girl who could fall in love and be happy where the goddess can’t…
She’s Senadina, but also could never be her, who has already suffered for centuries and lost her innocence. Remember the alternate history Helia who showed up and started throwing hands? The other Senadina is a similar being.
Anyway, back on track. Senadina attempts to trick Vita into killing her, but Vita sees through it at the last moment.
Sa may be dead, but Vita is a clone of her who carries her memories. When Senadina and Vita meet, two things happen: They both recall the memory of the shared Cocoon dream clearly, and Senadina clocks that Vita isn’t Sa, obviously arousing her suspicion.
Regardless of how hostile she’s being, however, Vita refuses to indulge Sena’s suicidal attitude, forcing her to show her around Difeng and reminisce so she can have a proper farewell. That’s the context for a lot of the flashbacks I’ve explained above.
They spend the next hour or so reading each other for filth, once Senadina sees through Vita’s provocation she realizes she’s not malicious, but playful, and that after her one wish came true so perfectly, she was left with nothing to make her feel alive. Vita also warms up to her, revealing a sad expression when she finally does have to kill her off, and regretting that she didn’t bring roses for a proper funeral.
A rather tragic last-minute friendship…
Hope that clears things up! Let me know if you have further questions.
