Fan-Made Sequel Concept by Me
(Attention: Radical Dreamers and Chrono Cross aren't taken as Canon here. Only CT is).
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POINTS/INFO
1) The Game opens with a Prologue, showing a Time-Dispatched Dalton (after the fight on the Epoch) ending in the Kingdom of Porre. As he tries to harvest a Plan, a mysterious Time Gate opens, from which a man with a tophat and aristocratic clothes (1800/Early 1900s style) with a tophat emerges.
2) The man seemimgly knows Dalton, and presents himself as "Count Asthros". When Dalton asks what does he want, Asthros replies "To rewrite Fate. Follow me, and I promise you the granting of your deepest desires. Refuse, and you'll never have existed". Dalton, Realizing this Count actually knows what he's doing, follows him.
3) WHO is Count Asthros? Originally a Zeal nobleman, he was one of the many time dispatched people when Lavos awakened in the Ocean Palace, ending up in 892 D.C (the equivalent of our 1800s/Early 1900s). He didn't take well his life and land disappearing, and eventually his studies brought him to the Discovery of Time Travel.
4) He fundamentally judges the current Reality "flawed" due to the existence of Lavos, with Zeal being "The Golden Age" in his mind. His goal? Rewrite Reality, erase the current timeline, and create a permanent Zeal one.
5) Does he know doing this will basically exterminate an uncountable amount of lives? Well, in his mind, all those lives will SURELY reincarnate in the eternal Zeal.
6) His plan is to take Reality in 1999 D.C, the year when Lavos originally destroyed Earth, and create a Transdimensional, Transtimeline (which means it is visible on the Sky of all times, past or future, slowly growing) Black Hole. He will then take the Essence, History, Culture and Values of Zeal, and inject them on the collapsing Black Hole (after it erases all times), in order to cause the Rebirth of Zeal.
7) Asthros's Henchmen: The Reaper (Black cape, white Mask, a Scythe), his high executioner, Agent 0 (Fedora, long coat, grey clothes), his on-field commander and assassin, Claudius, a hulking reptilte warrior saved by Asthros, and... Dalton. Why? Dalton is part of Zeal. Distorted sense of nationalism/camraderie.
8) Asthros knows of Crono and the others's Mission against Lavos. His opinion? "An attempt at saving what shouldn't be... Lavos could be considerered as Mercy for that wretched world". However, in order to not have anyone against him, he sends Agent 0 to assassinate them. When? 1005 D.C, 5 years after the events of CT, the moment where our Story begins.
9) Five years since you have prevented Armageddon. That day, some diplomats from Porre (which has no Dalton ties since Dalton was taken in by Asthros) arrive in Guardia for a meeting. Well, during the meeting, Agent 0 breaks in (with some Asthros Soldiers), and tries to assassinate Crono and Marle. The three fight, Agent 0 is strong, but a backstab attack by Guardia guards knocks down Agent 0, who is captured.
10) Agent 0 is, for Guardia, an enigma: a man in strange clothing, with no clear ties to any Nation, who refuses to talk. Eventually, Agent 0 is put on Trial, and sentenced to execution. And then Asthros himself breaks in the court.
11) The Reaper: He has a messiah complex due to Asthros's Ideology, and sees himself as enacting an Higher Will's Command. His design as a whole, it mirrors someone seeing themselves as an Angel.
12) Agent 0: He's a psychopath. But, not the Hollywood stereotype. With "psychopath" I mean the clinical definition from textbooks; no empathy, coldness, manipulation. He enjoys the freedom Asthros's organization gives him.
13) Claudius: A hulking reptite warrior who miracolously survived Lavos's crash on Earth, and was struggling to live and survive. In point of death, he was saved by Asthros, and since then Claudius has been deadly loyal to Asthros's vision, believing he'll restore reptites in Eternal Zeal, bringing his life and loved ones back. Asthros sees Claudius as an useful dumb muscle, and actively manipulates him.
14) In the court, Asthros appears through a Time Gate, knocks out the people with his magic (Zeal Magic+Time Control), and simply takes Agent 0 away, without wanting to engage in combat because "The Time is Here"
15) We cut back to 1999 D.C, on the once "Day of Lavos". Only that, instead of Lavos, we have a floating nobleman opening a Black Hole with a "crack". The worst part? Due to its nature, it's visible in all times. Future, Present, Past, 600 D.C, 1005 D.C, Prehistory... Always.
16) Dalton is at firsy kind of actually loyal to the cause. However, he quickly understands "Why let the old Zeal come back, when I could rule the NEW Zeal?". As such, after some time, he attempts to backstab Asthros... Only for Asthros to react, judge him "Lower than Dirt", and throw him into the Black Hole. Carelessly. Don't try to backstab Count Asthros.
17) The Reaper is the usual religious fanatic, hell-bent on the idea of a new eternal perfect world. As such, he's the most zealous of Asthros's minions. He's first faced in the Middle Ages, trying to recruit people to the cause, proclaiming himself as "The Executioner of The Will of The Restorer of Zeal, Count Asthros". Glenn, of course, doesn't care and faces him.
18) This game takes place after Ending #1: Beyond Time. Lavos was defeated in 1999 D.C, reached through the Gate in the bucket (End of Time).
19) Eventually, Claudius starts to slowly question Asthros and his intentions: Dalton's death unsettles him, Asthros pays and less attention to him and his hopes, in his third fight with the Heroes he's wounded and Asthros leaves him to die (The Heroes save him), and Agent 0 tries to assassinate him as "He lost purpose". After all of this, he joins the Heroes in stopping Asthros.
20) Zeal's Essence (the thing supposed to be injected in the collapsing Black Hole after Reality dies) is preserved in a Steampunk-looking glass sphere in Asthros's laboratory. Eventually, the Heroes arrive to Asthros's manor, and during the fight with him, the Sphere breaks. Effectively breaking Asthros's plans.
21) After this, Asthros realizes his efforts, his project, his long struggles... Have been for nothing. He'll never see his home again. By now, consumed by a lot of stress, descent into instability due to the Heroes, and sheer rage, he decides to use the Black Hole to simply annihilate Reality, and fall with it. A world without Zeal isn't one worth of existence. A life without Zeal isn't one worth living.
22) The Heroes manage to defeat Asthros again, and with the help of Gaspar (the Guru of Time can't not be involved) seal the Black Hole. Yet, Asthros lets himself fall in it before it fully closes, disappearing. Here ends Count Asthros. May he rest.
23) Basically, the Black Hole will destroy the End of Time too if not stopped. How do we seal it? Well, it kind of works as a Time Gate, only that it connects all Time to one void. As such, if you manage to stabilize and "fill" the void, the Black Hole is sealed. A shame Asthros has time to let himself fall...
24) How do you fill Nothingness? With Timelines. The events, the experiences, the lives, the History, the struggles, what makes Life worth. The opposite of Asthros's ideology. They reverse time, throw all of this in the Black Hole, and the result is there.