The point where things change:

One Piece: Episode 390-391

Demon Slayer: Episode 1 and Beyond!

The Crew was heading out to Shabondy to go shopping or something

Franky and Ussop were filling up some cola, and Sanji was being the biggest BAKA.

To be honest he was bored out of his mind and he just wanted to leave.

SO HE DID...

Ussop: Huh? ZORO!

Sanji: Earth to Zoro-Kun!

Both: Where are you going all by yourself?!

Zoro: Just For A Walk

Ussop: Stop!

Sanji: Don't you dare, you dawn Bastard! You always get lost!

This an Archipelago you know! We'll never be able to find you!

Zoro: I Ain't gonna get lost! As if anyone could get lost on such a straightforward island as these!

"All these trees are numbered," he said pointing to some trees.

Worst case, even a kid could make it back by asking for directions!

Ussop: Oh! I never expected you to have such street-smarts!

Sanji: We underestimated you! Sorry! Take Care!

Ussop: Make sure to ask for directions!

Sanji: Don't Trust Yourself!

Zoro: I don't know what their talking about. I just need to remember the number of the trees.

hmmm

Ah yes it's 1

Pffft and they think I'd get lost here what a joke

Little did Zoro know, is that not only did he get the number wrong ( It was #41 not 1),

He was also in a WHOLE NEW world of trouble ;)

Zoro: Eh, why did it get cold all of a sudden

The sprawling high bubbly Mangroves disappeared like smeared paint. Replaced with cold hard Oak trees covered in snow.

Zoro: Shit what the hell, how did it get so cold. It was like 90 degrees a minute ago. "All I'm wearing is a fricking shirt and some jeans," he thought.

I Gotta find a coat or else ill end up a Zorosicle.

Tanjiro was officially having the absolute worst day ever. All he was doing was chopping up some wood then BOOM

Their all dead.

Luckily for him his little sister Nezuko was still breathing.

BUT...

It turned out she was a demon causing her legs to get dummy thick without the squats.

But she was about to chow down on him like some seasoned Tanooki.

She started crying

Tanjiro: Nezuko

And just as he was feeling better this maniac with a sword comes up about to kill her.

Tanjiro was lucky enough to push her away in time but he had no idea who that was.

Tanjiro: Who's that? A sword

Giyu: Why are you protecting here

Tanjiro: She's my sister, I was taking her to get help. "Nezuko growls louder making the man slightly disgusted."

Giyu: You call that thing your sister. He then Charges towards them.

Tanjiro ducks, but finds his sister gone. He finds that Giyu has her.

Giyu: Don't move, My job is to slay every demon I find which means I have to decapitate your sister here.

Tanjiro: No wait, Nezuko hasn't hurt anyone. Back at my house, there was another scent I never smelled before. That's probably the one, who killed my family.

I don't know why she's changed into something like this, but still.

Giyu: It's really quite simple. She's turned because her wounds were exposed to demon blood. That's how the man-eating monsters multiply.

Tanjiro: Nezuko would never eat a human.

Giyu: You must be joking. If I hadn't gotten here when I did she would've devoured you.

Tanjiro: You're wrong she wouldn't hurt me, she knows I'm her big brother. And I won't let her hurt anyone. I'll turn her back into a human.

I WILL HEAL HER!

Giyu: She can't be healed, once you become a demon no one can ever turn back.

Tanjiro: And ill find it no matter what it takes. So please let her live. I'll hunt down the one who slaughtered my family. I'll promise I"ll make everything alright.

PLEASE! Just Let Her GO! PLEASE DONT DO THIS!

And This is where it changes

Zoro rushing from out of the woods 3 swords in tow.

Zoro: ONI-GIRI!

Giyu: What the...!

He was just able to block it, but he had to let go of Nezuko (Who ran back to Tanjiro)

Giyu: You fool the Demon's going to- GASP

Zoro: Just give your coat...

Or I'll cut off your skin!

Giyu is able to push away Zoro momentarily, readying his blade.

Giyu: I don't know who you are, but something's definitely wrong with you.

Zoro: Ju-Ju...st Gi-gi... ve me... coat. He said raising his swords

Giyu: "Fine" He said pulling out a ragged green uniform he didn't know he had.

But before he does he sees the demon protecting the boy and has hope (but keeps it inside)

Giyu holds out the gi and as Zoro goes to grab it, and then pulls it away.

Giyu: I'll give it to you on one condition

Zoro was literally freezing, injured, and started to get annoyed too.

Zoro: ye-yea what.

Giyu: I need to promise to keep that boy and demon ok and make sure they go to mount shigiri, look for an old man with a red mask, tell Giyu sent you, got it?

Zoro: "Yea yea sure." He said grabbing the coat and putting it on.

Giyu: As Giyu starts to walk away he adds " Oh yea and don't let her get any sun or she'll be lit on fire.

Zoro: "Wait what" but he already disappeared.

Dang what the hell did I just agree too.

Zoro looks at the boy and girl. The boy had a scar on his head and some cool earrings. The girl looks like she took some serious drugs she had veins all over her body and had a stick in her mouth.

Zoro: Hey boy is your sister ok?

Tanjiro: NO OF COURSE NOT! MY SISTER'S A DEMON AND THIERS NO WAY BACK!

Zoro: Alright calm down, where's your family anyways?

Tanjiro gave the meanest stare alive that even made Zoro recoil slightly.

Zoro: Jees alright fine could I at least help you bury them?

Tanjiro just sighed and nodded his head.

Later that day

Zoro and Tanjiro finished burying the bodies, Zoro decides to talk to Tanjiro a little bit

Zoro: So kid, what are you going to do now?

Tanjiro: Looking confidently he said "I'll get revenge for my family and find a cure for Nezuko"

In order to do that I must get stronger than that man who attacked me.

Zoro: Now that's a dream, If you don't mind can I ask for your name?

Tanjiro: Tanjiro and this is my sister Nezuko.

Zoro: "Roronoa Zoro." Standing up. " I'll Remember that name Tanjiro, come on we need to get to the mountain.

Tanjiro: Ai