WARNING: The following article contains spoilers for Episode 20 of Demon Slayer: Kimetsu no Yaiba, "Pretend Family," available now on Hulu, Crunchyroll and other anime streaming services.
Kimetsu no Yaiba established its rules for killing demons early on in the show: Someone wielding a Nichirin Blade needs to slice through a demon's neck. It's simple, and easy to understand. However, the latest episode of Kimetsu no Yaiba, "Pretend Family," reveals a new way to kill demons that could have major consequences going forward.
Although Tanjiro Kamado seemingly killed Rui at the end of the previous episode, the demon ended up using some of his tricks to decapitate himself and then reattach his own head just prior to the blow. This keeps him from dying, as he wasn't beheaded with a Nichirin Blade. Completely exhausted from using his breathing techniques, Tanjiro seems vulnerable and about to finally fall to Rui. However, Giyu Tomioka jumps in to save the younger demon slayer. He then turns his skills on Rui, using his Water Breathing Eleventh Form: Dead Calm. This is the first time that form has appeared, and Tanjiro previously indicated Tenth Form was the final form, meaning this new technique is beyond what he was expecting and thought possible.
Dead Calm allows Tomioka to easily evade Rui's attack. He then calmly walks forward and cuts Rui's head off. However, this time the demon is down for good, as evidenced by the extensive flashback showing how he went about assembling his pretend demon family and brutally enforcing a status quo amongst them. This leads to showing how he rescued Older Sister Spider demon from a mob of demon slayers and the relationship between the two.
From there, the episode picks up with Older Sister Spider, who is attempting to flee from the fighting going on elsewhere on Natagumo Mountain. She eventually bumps into another unnamed demon slayer and binds him up in a cocoon that will liquify him in a few minutes. However, as she's preparing to leave him to die, she encounters Shinobu Kocho, who shows a penchant for sadism. After Older Sister Spider begs for mercy and lies about how many people she's killed, Shinobu threatens -- in a gleeful tone -- to remove individual parts of her one by one.
Older Sister Spider tries to fight Shinobu, with the latter releasing her Insect Breathing Butterfly Dance to hit the former with a ton of tiny blows. However, Older Sister Spider realizes Shinobu's thin sword means she's not strong enough to actually decapitate a demon. Much more confident in her chances, Older Sister Spider prepares to attack Shinobu, when she's stopped dead by a mysterious force. Shinobu then reveals her blade is poisoned.
Although decapitation has been the typical way to kill demons in the show so far, Shinobu reveals she's a pharmaceuticals expert and has thus created a wisteria poison. As the series has previously established, demons hate wisteria and avoid it. The effects of demons getting near wisteria wasn't totally clear, but the poison proves them getting it into their bloodstream is fatal. The effects are also a bit different than those caused by decapitation. Shinobu remarks the body will rot, indicating victims won't dissolve like other demons.
This new way of killing demons could definitely prove effective in future battles and provide a lot of new ways to deal with the Twelve Kizuki. However, the "Taisho Secret" portion of the episode reveals Shinobu creates the poison inside of her sword's scabbard, a secret which is only known by her and her swordsmith. The relative secretiveness surrounding Shinobu's poison does raise questions about whether the poison will be lost if anything happens to her in the future. Still, the wisteria poison will likely prove valuable in Tanjiro's quest to collect blood from the Twelve Kizuki.
New subtitled episodes of Demon Slayer: Kimetsu no Yaiba air Saturdays on Hulu, Crunchyroll and other anime streaming services.