Some points to bring up before the story begins, so all of you don't get ultra confused.
1. Christianity is portrayed as 100% accurate here, instead of the perverted, twisted failure Atlus insists upon in order to simp for Neutral for the 9999999999999999999999999999999999999999999999999999th time in existence and also Chaos, aka the worst and second worst routes.
2. The story follows SMT1 and SMT4 fused into one single storyline, as per my headcanon when having played both. The established route is Law, aka the best route.
3. Isabeau is no longer Neutral, due to being brought back to the light by her now-husband, Dust (*cough*me;3*cough*). Furthermore, she is now the Messiah of Mikado, that being it's spiritual leader helping them to serve God and the head of all Samurai. She also lost her right arm to a demon attack and has a mechanical prosthetic in it's place.
4. Isabeau's katana is the Karyuken from SMT1, as she also takes on the SMT1 Heroine's role.
5. I headcanon the 1986 Famicom game The Mysterious Murasame Castle as a prequel to SMTIV's setting, with Isabeau being a distant descendant to Takamaru. He had been the one to forge the Karyuken, which was passed down through his lineage until Isabeau inherited it.
Isabeau looks at Taishang Laojung in displeasure. She remembers how he had harassed her and Dust about their decision to not be "Neutral" when they'd come upon him in the Ginza Underground District. She looks at him exhaustively, not wanting to have to deal with his screeching for the second time, especially after she and Dust had already banished the demons back to Hell. She crosses her arms over her chest as she looks at Taishang with annoyance.
"Oh, it's you. What do you want, Taishang?" Isabeau asks tiredly.
Taishang, not understanding the nuance of Isabeau's displeasure, smiles at her and bows before speaking in a respectful tone.
"Greetings, Mother Isabeau. I would like to offer a humble proposition to you, if I may." Taishang replies.
Isabeau relaxes slightly at that, her annoyance replaced with curiosity. She nods courteously to him, thinking he'll actually try to be civil for once.
"A proposition? Sure, I would gladly listen. What is it?" Isabeau asks.
Taishang, unsurprisingly, once again tries to convince her to stand aside like a good little "neutral" girl.
"Mother Isabeau, you have great power and authority in this world, yes? I would like to remind you of the importance of maintaining a neutral stance." Taishang replies.
Isabeau frowns deeply at his words, her annoyance returning as any good will she'd started to feel towards him vanishes instantly. She stands up a little straighter, staring at Taishang directly
"Maintaining a "neutral" stance? In this time? Is that all you can offer, Taishang?" Isabeau asks.
Taishang, like the usual dumbass he is, tries to lecture Isabeau that mankind is "better" on it's own without God or a reliance on deities, needing to be "dependent" on it's "own strength". It doesn't occur to him at all that, maybe, this newfound peace across Tokyo is a result of Isabeau and Dust having descended to it from Mikado as an act of God. His tone is preachy, as though he truly believes that preaching to her about the "importance" of Neutrality is the most productive use of her time.
"Mother Isabeau, I would also like to remind you that mankind is stronger when they are self-reliant. Relying on deities and other powers makes them weak. They must learn to stand on their own two feet to truly be strong." Taishang replies.
Isabeau's irritation grows with every word Taishang speaks. She listens to him, but her patience is quickly wearing thin. Her voice becomes more firm as she responds to him.
"Do you really believe that, Taishang? That mankind is stronger when they are self-reliant? That they should not depend on others? That relying on something greater than oneself makes them weak?" Isabeau asks.
Taishang nods, his bias against God and deities overriding any and all logic he has. To some, Taishang may even seem a little insane, but he's very much set in his ways as a "free willed man".
"Indeed, Mother Isabeau. Man must learn to be independent and strong, to stand on his own two feet and not rely on higher powers. That is the true path to strength and freedom." Taishang replies.
Isabeau clenches her jaw, her patience fully worn out. Her voice is sharp and firm as she speaks.
"That's a pretty narrow-minded way of thinking, Taishang. You do realize that depending on others doesn't always make someone weak, right? Sometimes, it's the opposite. Sometimes, it's taking a stand and depending on each other that makes people stronger." Isabeau says.
Taishang completely ignores her thoughts on the matter. He seems completely immune to the anger in her voice, instead continuing on with his preaching.
"Mother Isabeau, I believe it is time for you to embrace a more secular lifestyle. Those robes and religious symbols do not suit you. You should wear something more fitting of a strong, independent woman, without the constraints of religion." Taishang says.
He grabs hold of the sleeve of her robe, but Isabeau swats his hand off her with her prosthetic arm, her eyes flashing with anger as he thinks he can violate her identity as a godly woman in this way.
"How dare you touch me! And how dare you imply that I should discard my faith and religious beliefs! You think you have the right to decide what I wear and what I believe in?!" Isabeau asks angrily.
Taishang gives her a condescending look, believing that he's trying to lift her up out of her "religious delusions" and to be a "free thinking" person like himself.
"Why, Mother Isabeau, I am merely trying to offer you advice. Those chains of religious dogma are holding you back. You are stronger than this. You are stronger than your faith. It is the path to personal freedom." Taishang replies.
Isabeau's eyes narrow as Taishang continues to speak. She clenches her fist as she responds, her voice cold and sharp.
"You dare to call my faith "chains" and "dogma"?! You dare to say that I am being held back by my religion?! It is my faith and my beliefs that have made me who I am, Taishang! It has given me strength, hope, and purpose. You have no right to belittle my beliefs and tell me what is best for me." Isabeau snaps.
Taishang shakes his head, dismissing her beliefs with a tone of condescension.
"Mother Isabeau, you need to wake up to reality. Your faith in some so-called God is nothing but a fantasy. It is an illusion that is holding you back from reaching your full potential. You need to break free from these delusions and embrace the true path of Neutrality without religion." Taishang says.
Isabeau's eyes flash with anger as Taishang continues his condescending tone. She steps closer to him, her voice cold but firm.
"My faith is not an illusion. It is what gives me purpose and hope. I will not be so foolishly arrogant as to deny God's existence, unlike you, Taishang." Isabeau hisses.
Taishang gives her an arrogant smirk, thinking that he has the high ground in this little debate. He seems to get a perverse delight from belittling her like this.
"Please, Mother Isabeau, do you really think you "talk to God"? You think you are "the Messiah"? Do you really believe you are some "Chosen One"?" Taishang asks mockingly.
Isabeau takes a deep breath, trying to maintain her composure in the face of Taishang's arrogance and mockery.
"Fine, Taishang. Let's say that I embrace your "neutral" stance, that I reject God and my faith. What exactly would you have me be like?" Isabeau asks, testing his response.
Taishang smirks as he starts to delve into great detail. The entire time, he makes sure to say all this in a way that belittles Isabeau, treating her as just an object, a puppet. He waves his hands around as he speaks as though he's in some sort of trance, wanting to show her just how great his "enlightenment" is.
"Oh, Mother Isabeau, you will become enlightened like me. You will no longer be trapped by the chains of religion and dogma. You will become truly free, truly independent. You will become a true neutral being, unbound by any higher powers or spiritual beliefs." Taishang replies.
Isabeau's jaw tightens at Taishang's condescending tone, but she allows him to continue.
"Is that so? And what exactly will I do after I become "enlightened" like you? I'm assuming I won't remain a Messiah anymore. Or a Samurai." Isabeau asks.
He shakes his head and smiles at her smugly.
"No, you won't be a Samurai or a Messiah anymore. You will be a "free girl", a "strong independent woman", a woman that is free from the chains of "religion". You will be free to do as you please, unbound by any "religious" restraints." Taishang replies.
Isabeau bristles at Taishang's words, resisting the urge to physically lash out at him. She is seething with anger, but manages to maintain her composure, her voice tight and cold.
"So, I will be reduced to being just a simple girl. Just a mere woman without any role or purpose. I will no longer have any sense of responsibility or duty. That doesn't sound like enlightenment, Taishang. It sounds like being completely hollow." Isabeau says.
Taishang smirks and leans in closer to her, a smug smile on his face.
"No. Mother Isabeau, you will not be hollow. In fact, you will feel much freer without the chains of religion or duty holding you back. You will be free to serve men and be submissive, as a "neutral", as it is your true place. You will no longer care about your "duty" or responsibility to some imaginary sky daddy." Taishang says.
Isabeau's hands twitch, but her voice stays cold and biting.
"Serve men? Be submissive? Is that all you think my true purpose in life should be?! To be subservient to man?! How archaic! What if I don't want to serve men? What if I don't want to be submissive?" Isabeau asks disgustedly.
Taishang lets out an amused chuckle, feeling he's won this conversation and that she deserves to be "put in her rightful place".
"Why, of course you do want it deep down. That's the natural place for women, after all. And with no religion to "corrupt and hold back women", they will naturally be seen as the true subservient creatures they were always meant to be." Taishang replies.
Isabeau finally loses her patience finally. Her prosthetic hand violently clenches around Taishang's neck, pulling him off his feet. Despite her Christianity, Isabeau feels so much rage boiling inside of her at this hateful, sexist, worthless false prophet sent to deceive what's left of the humans she and Dust saved from the demons. She speaks lowly, her voice cold and venomous.
"You are a spineless... soulless... hate-filled insect. You think you have the right to demean and belittle women and religion?! You think you have the right to decide what is the "natural place" of women?! Women are not subservient "creatures" to be used and discarded by men! They are human beings, who have the right to decide their own place in the world! We are all human beings, Taishang, and we all deserve the same rights and respect. You are the delusional one, if you think otherwise. You are the one who is ignorant and foolish, if you believe in some outdated, bigoted concept of the "natural hierarchy" of things." Isabeau hisses.
Taishang's face slowly begins to turn blue from the heavy metallic grip on his throat, the coward unable to speak as her grip doesn't let up around his neck. When his face slowly becomes purple, Isabeau finally releases her tight grip on his throat, dropping him roughly on the ground and letting him gasp for air. She steps back, still seething with anger, but feeling a sense of righteousness in her mercy.
"Count yourself lucky I have the grace to show you mercy, you hateful fool. You are not worth soiling my hands with your blood." Isabeau says dismissively.
She turns around to depart, but Taishang sneers and spits at her back.
"Ungrateful wench! You think you're "justified" in your obsession, do you?! You're nothing but a stubborn, arrogant girl! You will learn your place one way or the other!" Taishang snarls.
He grabs the hilt of his sword, wanting to take her by surprise. However, Isabeau realizes what he's doing and quickly unsheathes the Karyuken. With lightning fast speed, the flaming katana immediately severs his sword arm, instantly cauterizing the armless stump from the extreme heat. Taishang lets out a pained scream and stumbles backwards as his sword arm is severed. He falls to the ground, clutching at his wound, shock and pain written on his face.
"You… you… cut off… my arm…" Taishang moans, unable to speak clearly through his pain and shock.
Isabeau stands over Taishang, her sword still ablaze with holy fire, her eyes filled with a cold, stern determination. She looks down at him with a mixture of righteous indignation and a hint of pity.
"That's right. I cut off your arm because you dared to attack me from behind, like a coward and a snake." Isabeau says.
Taishang gasps out between ragged breaths, his face contorting in pain. He tries to protest, but the pain and shock make it difficult for him to form coherent words.
"Y-You… you're… insane…" Taishang rasps.
He can hardly look at the cauterized stump that was once his right arm. He knows he'll never be able to use it again, but he doesn't have to worry about the thought long as Isabeau plunges the sword into his cold, black heart, the blade severely burning his body and officially ending the life of this worthless false prophet. Isabeau takes a deep breath as she watches Taishang perish, his eyes losing their life as the evil light fades from them. She steps back, feeling a pang of shame and pity for the fallen man, knowing what lies ahead for him in the afterlife. She removes her sword from his ruined body and lowers it, silently sending a final prayer for his soul before sheathing the Karyuken, her face solemn but resolute.