Episode 29

Should Have Been (本当なら) is the 29th episode of the Kimetsu no Yaiba TV anime series, and the 3rd episode of its second season.

Synopsis
Tanjiro, Nezuko, Zenitsu and Inosuke join Rengoku on the Mugen Train. Having heard that there may be demons on the train, they are on high alert, but they find themselves falling into a slumber. Within his dream, Tanjiro is reunited with his long lost family. However, it is soon revealed that this is a trap set by Enmu (Lower One).

Plot
Enmu stands on the locomotive on the Mugen train and mutters to himself about lucky they are to die while sleeping. He tells of how humans are all the same, Demon Slayers or not, they are led by their heart, their spiritual core; once destroyed, they're trapped in a sleep they can never awaken from again. He senses that Tanjiro Kamado continues to fall deeper into his slumber as he dreams he is reunited with his family.

As Zenitsu Agatsuma falls deeper into his sleep, he dreams he is in a peach tree forest, with Nezuko as his girlfriend. He carries her on his back when she claims she cannot swim a river and they traverse the mountains with his Thunder Breathing. Inosuke Hashibira dreams he is leading a cave expedition, accompanied by Nezuko, "Ponjiro" and "Chuitsu" as his underlings. They encounter the beast that is the Mugen train in the cave and proceed to charge ahead to attack it. Kyojuro Rengoku dreams he is at the Rengoku Estate, sitting before his father Shinjuro to tell him of his promotion into a Hashira. Shinjuro dismisses his news and calls it worthless, adding that he believes Kyojuro would never amount to anything, as does he. Kyojuro walks out and sees his brother Senjuro, who asks about their father's answer, believing maybe he could be acknowledged as well should he become a Hashira. Kyojuro mutters to himself that his father never acted as such in the past; he once held the mantle of Flame Hashira but unexpectedly quit. And he too was once enthusiastic about training him. Kyojuro refuses to dwell in this and instead encourages Senjuro that despite their father's lack of acknowledgement, he will continue to be proud and passionate. Senjuro tears up when his brother mentions he as him as moral support.

The four children tasked by Enmu manage to enter their dreams, enabled by a rope made of his Blood Demon Art. Enmu explains the dream world contains a border to the realm of the subconscious, and they can pass it once they enter the dream and locate its edge; instructing them to destroy their spiritual cores to cripple them. The girl tasked with Kyojuro finds the edge and crosses the border with an awl made with Enmu's bone. As she traverses the unusually hot and fiery realm of subconsciousness, she manages to locate his spiritual core. When she moves in to destroy it, Kyojuro suddenly grabs her throat whilst both are still unconscious, causing the girl in the realm to be crippled and unable to move; she becomes stunned and amazed at his incredible survival instincts despite being fully asleep.

Tanjiro plays with Rokuta while his mother Kie decides to make them rice crackers as a treat. Takeo becomes annoyed and too wants rice crackers, causing Hanako and Shigeru to add that they themselves want some as well. Meanwhile, the boy tasked with Tanjiro has entered the dream and overhears the Kamados. Outside, Tanjiro chops down wood for a fire, but when he fills the basket and begins walking home, he mutters, "Nezuko, let's go". Suddenly confused at his words, he looks back at his basket. He returns home and enters the living room, before looking around and asking on Nezuko's whereabouts. Takeo answers she went out to pick vegetables, causing him to grow worried since it's day. The concern confuses his siblings, but before he can explain, Kie asks him to fetch water for a bath.

As he walks to the river, he tries to make sense of his unusual remarks; while doing so, he unexpectedly sees Nezuko's box in the corner of his eye but it vanishes when he takes a closer look. Dismissing it as simply a tool box, he reaches the river and fills his buckets. Suddenly, he sees his reflection warning him to wake up; it pulls him into the water and claims he is under attack, causing Tanjiro to realize he truly is still on the train and asleep. The reflection begs him to wake up and fight, causing him to return to his home. In the living room, Tanjiro is now fully aware he is in a dream but is unable to see a way to escape. On the train, Nezuko falls out her box and sees Tanjiro and the Demon Slayers all unconscious. She sees Tanjiro whispering he needs to wake up and tries numerous ways to do so, before she grows frustrated and head-butts her brother to awaken him. Failing to do so and bleeding from the impact, she begins to cry and tearfully tries again, causing her Blood Demon Art to activate. In the dream, Tanjiro becomes engulfed in Nezuko's flames, to the confusion and worry of his siblings. He smells her blood and becomes covered in more fire, regaining his Demon Slayer uniform and Nichirin Blade, realizing he is slowly waking up. Takeo and Hanako ask if he is alright; Tanjiro answers that he needs to leave and apologizes.

Running out the house, he sprints into the woods, believing he needs to find a demon within the forest. To his shock, he hears Nezuko asking where he is going, having returned with a platter of vegetables. Hearing her voice again, he begins to tear up, whilst his family arrives to question him. Kie asks if he is all right but he doesn't answer, to his siblings' concern. Instead, he wishes he could stay here, as his voice begins to break; he wishes he could go back and by all rights, he is meant to do so, returning to his life of making charcoal and looking after his family. If it never happened, they would all still be alive and Nezuko still human. Instead, he walks on ahead to leave them, accepting their deaths and that he could never be with them again. Seeing his oldest brother leaving, Rokuta cries out to him and tries to chase him, causing Tanjiro to cry and apologize that they can never be together again. He runs out further, whispering they will always be in his heart no matter what. Meanwhile, the boy who entered his dream crosses into his realm of subconsciousness but finds it unusually calm and peaceful.

Outside the train, Enmu becomes confused that the children seem to be taking a while, since none of the spiritual cores have been destroyed yet, but doesn't dwell on it. Tanjiro realizes he is trapped in the dream but senses the scent of a demon in the air. Wondering how he will save everyone he is suddenly met by his father, Tanjuro, who appears for a moment and tells him to take up his blade, as there is something he needs to cut. He unsheathes his sword and realizes what he must do to wake up and escape the dream. Steeling his resolve and positioning the blade, he cries out and pushes the sword into his neck