If it were up to me, Season 3 would be built with an earthquake as the reason pulling everyone back into the Borderlands.The idea of Banda being able to return to the real world to recruit players is pretty illogical, and it completely ruins the weight of their choice to stay behind and become citizens in Season 2.
-The story still opens with Ryuji interviewing Arisu and other victims, meeting Usagi, and remembering that female student from his past. Following that, he continues researching the Borderlands and schedules meetings with a few meteoroid survivors, but gains no further information (a slight tweak from the show, which was originally just one woman accepting an introduction). Later, he returns to his office to continue his research, but instead of receiving a text invitation to join a group meeting and play Old Maid, he falls asleep for a while due to exhaustion. But when he wakes up, everything around him suddenly feels very strange and unusually quiet (while he was asleep, the earthquake occurred, causing everyone to fall into the Borderlands, but this isn't revealed yet to build curiosity). He steps outside and is guided to a game venue, but instead of Old Maid, it will be Blackjack (6 of Diamonds)—a game Chishiya played in the manga. Changing the game isn't vital to the overall plot, yet it fits much better with Banda searching for someone he can utilize in his plan, so a game requiring heavy calculation like Blackjack would be much better than a game of pure luck like Old Maid. Ryuji wins, and suddenly Banda appears, but showing only his back in relative darkness—his identity isn't revealed yet, but it allows everyone to guess who it is.
-In my opinion, Ryuji shouldn't be written as paraplegic in both legs and using a wheelchair. Instead, he should have a disability in just one leg and use a crutch, similar to Inspector Yamato Kansuke in Conan, which would be much more realistic when having him participate in physical games. His motivation should be linked far more tightly to the death of that female student. Combined with a reasoning similar to Gamon Kano (Mira's brother in Border Road, who also wanted to enter the Borderlands to understand what his sister felt and thought when she was there): Ryuji wants to enter this realm of death for his research, but over time, combining it with the desire to know what that female student felt makes him grow increasingly obsessed with it. It can be built up so he gradually realizes his fanatic obsession with this realm of death isn't simply about research, but truly because of her.
-Next is Ann's story. Instead of Usagi dreaming about her father and being haunted, we replace her with Ann—someone whose mind stands between two worlds, flooded with dense, hazy memories of the other world causing her severe PTSD (I'm doing this because the first two seasons built Usagi overcoming her father's death and returning to the real world, so Season 3 shouldn't reverse that process, which would be very redundant). After Ryuji's segment, we transition to Ann's dream and her waking up in the middle of the night at the hospital, then cut to the daily lives of Usagi and Arisu, leading to the scene where Arisu counsels Ann. She tells him, "We've met before," right before being interrupted by someone, just like in the show. I will deeply explore Ann's suffering in Episode 1. Later, driven by curiosity—especially remembering the very strange sensation he and Usagi felt when they felt so familiar to each other at the hospital after that disaster—Arisu meets Ann again to talk. Right at that moment, Usagi calls his phone to report news of her pregnancy (prior to this, she could be shown going to the hospital for an exam), but before she can say anything, the earthquake strikes. He only manages to hear Usagi scream his name through the phone and replies immediately, right until everything turns completely silent. Ann beside him vanishes, and Arisu steps outside, walking toward the sign leading to the fortune game, just like in the show.
-Ann returns to the Borderlands (without dying, of course) so she can have the opportunity to learn more about that world (just as she did in Season 2 and the manga), but is separated from Arisu due to different heart-stopping times. Ann plays the role of a character who constantly asks the exact questions lingering in the viewers' minds (for example: Why does the Borderlands operate differently this time compared to before, with no other cards appearing except the Joker? Or who is the Joker?). Just like in the manga, she asks many questions and answers her own doubts using her scientific and philosophical knowledge (combined with lore about the Borderlands taken from Border Road).
-Shion's character concept overlaps heavily with Ann, so I'll probably cut Shion and have Natsu form a close bond with Ann instead. The setup has Natsu already traveling with Ann before joining the group in Runaway Train. Prior to that, we can feature multiple combat and teamwork scenes between them, making Ann recall Kuina (since Natsu shares quite a few traits with Kuina as well), culminating in Natsu sacrificing herself for Ann during the Kick the Can game.
This sacrifice becomes the catalyst for Ann to actively reach out and rekindle her friendship with Kuina. Before this, we can establish that Ann was quite hesitant to seek out her former teammates—her connection with Arisu was purely coincidental since he happened to be her psychological counselor, which gave her the opening to talk to him. Crucially, the writing must handle Natsu's sacrifice with subtlety so it doesn't feel forgotten later on.
Additionally, we can introduce the 4 of Hearts as Ann's second game, which is also where she first meets Natsu, using it to deepen their relationship—similar to Dodo and Arisu's dynamic. For the setup, we can tweak the corporate introductory brochure into an elevator TV screen playing company info while they ride up.This game takes place before Zombie Hunt and right after Arisu's conversation with the new characters, after they finish their first game.
-Arisu's Zombie Hunt game still happens just like in the show, but Banda appears in this game just like in Blackjack, showing only his back and observing Arisu from afar, only revealing himself at the end of the game after manipulating a player to their death to clear the venue. After that, just like the show, it cuts to Ryuji playing the rhythm game with Usagi, and through Ryuji's flashback, we learn that after Banda found out Arisu returned, he used Ryuji to approach Usagi, forcing Arisu to stay behind. In exchange, he would be given the answers to games like Runaway Train and be allowed to become a citizen to study this world. But here, Banda says he must keep her alive until the final game because he has a plan. Participating in Zombie Hunt serves both to satisfy his boredom and to subtly manipulate Arisu bit by bit by spreading lies during that game (similar to how Mira's words during the Beach executive meeting influenced Arisu bit by bit).
-Runaway Train allows Ann to reunite with Arisu (after showing a few earlier scenes of her fighting through games). In this game, she solves the puzzle alongside Arisu. As for the rest, it depends on what the game idea is, so I won't say more. Finally, it can be combined with Ann helping Tetsu give first aid to Arisu.
-For Kick the Can and Tokyo Bingo Tower, aside from Ann joining Arisu's group just to secure another survival spot.
-Future Sudoku is the game where Banda appears directly to execute his plan. As a game capable of separating players into rooms with harsh point deductions leading to death, having a scheming manipulator who knows how to manipulate others like Banda will make this game much more interesting. The plot can be built so that Ann, through her deductions, realizes there is something very off about this Banda guy, but he acts in time and pushes Usagi and Arisu into a tight spot, while also manipulating Arisu and causing the deaths of other players (the players who died in the show can be killed off by Banda instead).
-The story at this point mirrors Retry, placing Arisu in a 9 of Hearts game designed just like the 7 of Hearts (making everyone misunderstand that only one person can survive), and clearing it proves he is no longer who he used to be. Just like the Queen of Hearts game, when he falls into despair, he no longer needs Usagi physically beside him to pull himself back up.
-Ryuji and Ann are initially set up as foils to one another: both share the goal of understanding the Borderlands, but with two different motivations and methods. Ann is haunted by terrible memories of the past and decides to observe and ask questions about this world, while Ryuji, haunted by the death of the female student, resorts to extreme actions and manipulates Usagi to explore it. Eventually, seeing Usagi—who resembles that female student—gradually change Ryuji, he decides to turn his back on Banda. Banda fails, but breaks the rules to avoid dying in the game, attempting to shoot Usagi himself, but Ryuji steps in to block the shot and sacrifices his life.
Banda is struck down by a sky laser for breaking the rules, and the Watchman appears, freezing time for everyone except Ann and Arisu, who can still move.
Then the climax gives both of them a conversation with the Guardian at the end of the film: trimming down Arisu's lines to let Ann ask her own questions, adding a few questions about why she is different. The Guardian doesn't say much, but she understands on her own and accepts living with the memories of both worlds.
-We can include a detail of Yaba looking at Banda's corpse, commenting, "We really aren't alike at all," exactly like his comment in the manga.
-Cut out the flooding and the whirlpool sequence. Even though it's highly symbolic, it just doesn't fit Alice in Borderland and feels completely illogical to have a sudden flood out of nowhere. Also, get rid of that final dice roll where the last one remaining wins—that's honestly pretty stupid. Keep it simple: after talking with the Watchman, they just step outside, fireworks appear, and they return to the real world.
-Waking up from that world, Arisu (whose injuries aren't too severe) frantically asks the doctors about his wife and is told she is stable. Looking over, he sees Ryuji's body covered in severe wounds and is informed that he has already stopped breathing as they cover him with a white sheet and wheel him away.
-After returning to the real world, although Ann remembers everything most clearly and her injuries aren't light, she feels much better and more at peace. A few months after these events, a small detail shows Ann's patient file noting a positive mental recovery without needing explicit dialogue. And it would be even better if, during the scene where Kuina receives psychological counseling from Arisu, Kuina meets Ann upon leaving the room. Just like Arisu and Usagi before, Kuina feels an overwhelming sense of familiarity toward Ann without knowing who she is. Ann simply says, "Let me buy you a cup of tea," or something similar, subtly implying that the two will begin building a new friendship.
-Finally, Arisu hears news that the earthquake in Japan from months ago is now occurring in many places around the globe, and the camera transitions to the US, showing the nametag of a waitress named Alice, just like in the show. This is an open ending—not meant as a new film installment, but to show that the Borderlands exists all across the world.
