What if tanjiro got the carnage symbiote?

The train

Tanjiro leaves as he heads back to tamayo's house.He walks on to see the mother in new clothes.
Tanjir:You look nice.
The woman blushes.
Mother:Th-thank you.
Tanjiro:Where is Rui?
Mother:He's in the backyard.
Tanjiro heads to the backyard and sees rui training.
Rui:Greetings master.
Tanjiro:What are you doing?
Rui:Training.You showed me that they are more powerful things out in the world,I simply wish to be prepared.
Tanjiro:That's smart.Come with me.
Rui follows Tanjiro as they go to see Tamayo again.
Tamayo:Hello Tanjiro,you have returned.
Tanjiro:Yes.I need to ask you something.Do you know of any other demon's whereabouts?
Tamayo:No,I am afraid I do not.
Tanjiro:That's okay.
Rui:Your looking for more demons master?
Tanjiro:Yes.Meeting you opened my eyes.All this time,I was so concerned about the demon in my family that I forgot about others.But meeting you reminded me that demons are causing suffering,suffering to innocent people who don't deserve it.I am not a hateful person, but there is one thing I hate,and that is someone who tramples upon the lives of others for themselves,someone who decides what they want is more important and show no regard for others.I won't stand for it!
Tanjiro clenches his fist.He then takes a deep breath and calms himself.
Tamiko:The point is,I'm not going to ignore the families and people who have been hurt by Muzan anymore.I'm going to tear his empire down,and then...I'll take his life.
Rui:In that case,I know a demon we can start with.However,he's very powerful.
Tanjiro:However powerful the demon may be, they're no match for me.
Rui:I didn't believe so either.Very well,I will take you to the demon.
Tanjiro:Let's go.
The two walk to the exit door.
Mother:Your leaving again?
Tanjiro:Don't worry,I'll be alright.I'll come back.
Tanjiro rubs the mother's hair and walks out with Rui.Rui closes his eyes as his appearance begins to alter.He no longer looks like a demon,but a human.
Rui:Follow me master.
Rui takes off at high speeds.Tanjiro crosses his arms and dashes in tow.In mere minutes the two arrive at...

A train station?
Tanjiro:A demon resides here?
Rui:Yes,but of course,he only emerges at night.
Suddenly,tanjiro hears a familiar voice.
Zenitsu:Tanjiro?
Tanjiro turns around to see Zenitsu and inosuke.
Tanjiro:Hey guys,weird seeing you two again.
Rui:Who are these people master?
Tanjiro:Rui,these are my friends,Zenitsu and inosuke.What are you two doing here?
Inosuke:We heard they had another demon on this weird steam thing.We came here to get rid of it!
Tanjiro:Me and Rui were also here to slay the demon.
Zenitsu:Is that who this is?
Rui bows politely.
Rui:Greetings,friends of my master are also friends of mine.
Inosuke:Hehe!So the trio is back at it again! With the three-
Inosuke looks at Rui,who's just standing there.
Inosuke:With the FOUR of us,nothing can stand in our way!Let's do this!
Inosuke rams the train with his head.
Zenitsu:You idiot!I keep telling you that's not how it works!
The four finally board the train.As they enter they see another demon slayer,he is sitting and eating food.