With the release of Chainsaw Man chapter 212, the manga saw Denji join Death Devil's alliance to fight the War Devil. Just as Denji was wondering what he was going to do about Asa, Yoru, and the upcoming war, he received new information about the Death and War Devil from Fumiko Mifune.
The manga's previous chapter saw the Death Devil explain to Denji why they needed to defeat the War Devil. However, as expected, Denji refused to believe that "Li'l D" was the Death Devil. In response, Li'l D raised her uniform, revealing her open belly to Denji. While Denji did not care about Li'l D's belly, he agreed to trust her.
Disclaimer: This article contains spoilers from the Chainsaw Man manga.
Chainsaw Man chapter 212: Mifune requests Denji to support Yoru

Chainsaw Man chapter 212, titled Really Good Girl, opened with Miri Sugo explaining to Denji the three strategies they had come up with to deal with the War Devil. However, Denji did not listen to a single word he said, as he was busy ogling the Death Devil. Just as Li'l D dropped her uniform, Denji snapped out of it to hear Miri Sugo asking him to rest in the nurse's office until it was time.
Chainsaw Man chapter 212 then switched to Denji lying on a bed in the nurse's office. He was wondering how a war was going to break out if he didn't do something about Yoru and Asa. That's when he realized he did not hear a word of the second half of Miri Sugo's explanation.

Just then, Denji remembered his kiss with the War Devil Yoru and the sight of Death Devil Li'l D's undergarments, wondering if it was okay to please himself in the nurse's office. Just then, Fumiko Mifuno responded to him from under the bed.
Fumiko Mifune explained to Denji how the Death Devil was using her. If Denji helped the Death Devil defeat the War Devil, it would be rather easy for the Death Devil to wipe out mankind, as in the prophecy. However, Denji had a tough time accepting this conflicting information, as he believed Li'l D was a good girl for carrying him to the school.

In response, Mifune explained that the Death Devil had already killed several of her Public Safety colleagues and even herself multiple times. When Denji was confused about how Death Devil killed her multiple times, Mifune explained that at age 14, she had made a contract with the STD Devil. The devil's power essentially saw any human she mated with to turn into Fumiko Mifune in mind and body. After Mifune made the contract, she mated with several people around the world, creating one Fumiko in every country.
With all the chaos, Fumiko knew that her numbers had steadily fallen. However, they were also able to routinely exchange information with each other. Wars had broken out around the globe even without the War Devil's involvement. So, considering that the world was going to be engulfed in war anyway, did it not make sense for the War Devil or Denji to defeat the Death Devil? While such a development would not see an end to war, mankind could live on forever.

Lastly, Fumiko Mifune infused a question in Denji's mind. Why didn't the War Devil turn Denji into a weapon yet? While Denji did not know the answer to this question, Mifune believed that Yoru was in love with Denji. Hence, if Denji defeated the Death Devil, he should be able to secure a happy life with the War Devil.
Just as Denji was trying to absorb that information, Mifune asked Denji to ask the War Devil to extend mercy to her as well. In return, Mifune handed Denji a risque photo of her. Upon seeing the picture, Denji labelled Mifune as a "really good girl."
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