In Chapter 133 of Chainsaw Man, Yoshida told Denji that Public Saftey would kill Nayuta if he transformed again.
Despite this threat, Denji decided to continue being Chainsaw Man because he wanted both the fame from that, and to take care of Nayuta.
However, the beginning of Chapter 134, “Ordinary Happiness”, shows that Denji is beginning to doubt his resolve.
Whereas we once saw him proud to hear people talk about Chainsaw Man, in both good and bad ways, now we see him wander the halls of his school and the city streets, looking more and more depressed at every mention of his alter ego.
He does not even look happy that night when he is drying Nayuta’s hair and she tells him that members of the Chainsaw Man Church are fighting the police.
He even tells Nayuta that the Church’s days are numbered because he won’t be transforming anymore, as the fear of what will happen to Nayuta if he does has got to him.
This shows exactly how important Nayuta is to Denji because, prior to this moment, it seemed that Denji being recognized as Chainsaw Man was one of the most important things in the world to him.
Denji now tells Nayuta that he is content because, “nothing beats a normal life.”
Nayuta questions this, asking Denji if he really feels that way, which is quite similar to Kobeni asking Denji if he wants to be normal in Chapter 92.
In fact, I would say that Fujimoto is making a direct parallel to that scene because, just as Denji was inspired by people cheering for Chainsaw Man on the TV after Kobeni questioned him about a normal life, he now sees something entirely different on the TV after Nayuta questions him about the same thing.
On the TV, we once more see that Haruka is being questioned about the Chainsaw Man Church but he responds well to the drilling questions.
Then he gets one that should throw him off, “It’s not as though he (Chainsaw Man) gave you them (instructions) directly, right?!”
Rather than be thrown off, Haruka instead says that Chainsaw Man has guided him and offers to call him for everyone.
Excited, Denji runs for the phone, ready to pick it up, only for the Imposter to walk on stage and declare that he is Chainsaw Man, much to Denji’s shock.
We still do not get a good look at the Imposter’s face, since it is hidden behind his cap, but we can see that he has dark hair and stands tall, making me think that he might be Seigi Akoku from the Devil Hunter Club.
Whoever he is, the Imposter claims that he recieved his power from the Justice Devil and fights to create a world without Devils where there will be an Adam and Eve.
Before he can explain to the reader why Adam and Eve are required, Denji cuts him off by shouting in outrage over someone stealing his identity.
He then breaks down into tears and Nayuta comforts him, ending the chapter.
As for the Imposter, I will admit that him showing up did throw a wrench in my previous theory that he was working against Fami.
I figured since he helped Denji and Asa escape when Fami was trying to kill them that they were on opposite sides and that the mysterious figured who talked to Haruka last chapter was the Justice Devil.
Now it seems that it was the Imposter and he and Fami are actually working togethor.
I also can’t help but think that Yoshida may have a role in all this, since he threatened Nayuta’s life if Denji transformed again and now, as soon as Denji is considering hanging up the Chainsaw Man mantle, an Imposter appears to take his place.
I do wonder if Asa will buy the Imposter’s ruse, however, because there is a theory that she will know he is a fake because Denji told her he was only interested in sex while the Imposter speaks so benevolently.
It is a humorous theory but I think it could turn out to be true.
As for what comes next, I am uncertain about that.
Denji could either transform again to prove the Imposter a fraud, or he could decide to live a normal life, though Asa and Yoru will most likely pursue the Imposter, even if they do know he is not the real Chainsaw Man.
“Ordinary Happirness” is a solid  Chainsaw Man chapter, which is clearly building up future events for the story, whatever they may be.