My Upgrades Are Invincible

I announced my presence in the main battlefield by kicking Muzan in the back of the head with a black flame coated heel kick and with the force of my bringing said heel onto his head with all the force of my descent the demon king's head literally bounced atop the rock they were fighting upon as all the soil had long ago been blown aside.

"I got Muzan you deal with your brother!" I yelled at Yoriichi who nodded thankfully at me and continued to combat with his older brother as I felt he would be happy at the end of day if anyone killed Muzan but his brother turning into a demon was a deep shame to his family, so he would want to deal with him personally.

Even as me and Muzan clashed in a battle of the titans with me cutting off his bladed whips, he would almost instantaneously regrow them without any care, but I could tell he was feeling the strain of generating so much biomass as well as wasting the biomass that he was passively losing even closing to my flame wreathed form.

Unfortunately, anyone or anything except the upper moons and the Hashira would die if they came within my flame's radius or around Muzan's wildly swinging whips as I chased down Muzan with him actually dodging around me and wanting to attempt to make this a battle of attrition as he knew I had killed Nakime so he wouldn't be able easily escape.

"Did you become a demon or something Yoriichi, if so, that would make you the biggest hypocrite? Or are you some foul demon art who was able to puppet my brother's essence." Kokushibo snarled as his inferiority complex reared its head and Yoriichi could only sigh at how his brother has fallen.

"My Brother Michikatsu, you have truly fallen into the pits of hell..." Yoriichi said tiredly as he dashed around one of the moon beams Kokushibo slashed at him and then used a front flips momentum to cut off one of Kokushibo's arms.

"I have abandoned long that name when I became a demon! There is only Kokushibo now! If you were never born, mother wouldn't have gotten sick, and father would never have been conflicted on who to pass our household onto!" Kokushibo screamed out hysterically as Yoriichi's inhuman grace and strength made a mockery of the strength he had gained over centuries being a demon.

Even as I was fighting Muzan I could hear Yoriichi's heart break and firm into steel as he responded to Kokushibo's ravings. "Very well... Then demon named Kokushibo, I am going to cut you down now." He said solemnly cutting off any prior bonds of blood they may have had.

I was no longer able to continue paying a bit of attention to their battle as Muzan had snapped at the constant frying by my flames and mutated into a massive baby bigger than an elephant which tree trunk thick bladed tentacles with mouths lining the sides of the tentacles.

"I came here to fight demons. Not Bloodborne monsters!" I yelled throwing several Holy Hand Grenades at the screaming mass of flesh as I didnt even want to get close to it with how I couldn't cut through the two-meter-thick flesh tentacles without the blades and mouths trying to grab ahold of me.

But despite them being called demons the holy attribute didnt do all that much but thankfully the grenades made several large craters in the flesh of Muzan's mutated form.

Muzan collapsed for a few moments allowing me to catch my breath, but I could see his flesh visibly growing where the craters the grenades landed so I flashed in front of the head of Muzan and then used a fire coated space blade to split the mutated monster in half.

"No! I shall not die! I am eternal!" Muzan's monstrous form screamed, and I was honestly very curious how he could even speak with how I had split him in half. But just like last time I had split him in half from top to bottom I went to move his halves away from one another to burn them.

"We got this half Jake!" Tengen Rengoku and Gyomei yelled and as I looked over at them, I saw Rengoku and Tengen helping bind Muzan around onto Gyomei's chain and then with a yell they rolled the writhing form away from the other half and fell upon it chopping into the screaming pile of flesh with their Nichirin blades.

"My demons feed meee!" A monstrous voice screeched out and then the other demons matched his screech by screaming in agony as their flesh bubbled and only Kokushibo was left alone as all the surviving demons exploded into a thick bloody mist which instantly flowed into Muzan's body despite me trying to burn away the mist, but it was so thick that it was like gelatin despite it flying towards Muzan.

"That's the biomass from all the demons and all the people the demons had devoured over the centuries." Shinobu explained as she landed beside me, and I saw all the other Hashira standing around Muzan as he screamed and wriggled out of Gyomei's chains before assuming a much larger form.

'From a Bloodborne horror to a fucking Armored Titan...' I deadpanned mentally seeing the now twenty-meter-tall form of Muzan who was armored with blue bone plating similar to what Gyokko had so I assumed it was going to be around that stupid diamond hardness Gyokko had.

I as an experimentally threw a space blade at him as he moved with deceptive speed to smash Gyomei and my space blade looked to only cut a couple inches into the half a foot thick bone plating into on his chest and even more worrisome was the collar of bone plating surround its heck which honestly looked like Muzan had roll of blue toilet paper or something around its neck as the armor visibly protruded from where the weaker neck was.

"Shinobu we are likely going to need you to poison and weaken him." I said blasting off to shoot flames and burnt out the large eyes of the naked and basically genderless form of Muzan.

But even as we pummeled him and literally tore huge chunks off the monster, we weren't able to do a killing blow with the massive amount around his neck which healed any gouges I made with space blades.

'Am I going to have to wait this fucker out till the sun comes up...' I thought feeling exhausted from the extended high intensity battle as only the battle against the Behemoths and Alfia was this draining.

But the problem to that thought was the fact that Muzan attacked us only a couple hours past sundown so there was a solid eight more hours minimum before any sun light reached over the horizon.

Thankfully my worries were cleared as Kokushibo died instantly as Yushiro came out of his invisibility demon art with a fucking blunderbuss of all things and blasted off Kokushibo's head with what I was guessing to be a Nichirin Slug.

Even Muzan paused seeing his trusted lieutenant being abruptly assassinated, but his reaction made me think of another scorned woman as the large titan Muzan vomited literal gallons of blood and we all saw Tamayo walk out of the shadows with several empty syringes which I had filled with fused toxins and poisons previously in return for helping Nerine.

"Damnit Tamayo! I spared your life, and this is how you repay me! With betrayal!" Muzan screamed as the Wisteria flower poisons worked in concert to destroy the Demon Kings regeneration and his large form started melting.

"I have never been loyal to you... I had hypnotized myself from the moment I came out of the feeding frenzy that killed my husband and children... I have devoted my immortal life to bringing you low and no price is too much to pay." She announced proudly and I was reminded about her sword she kept for grooming a husband to kill Muzan and how that could have easily been the Mist Hashira with his talents and even being related to Yoriichi. Not to mention how she was willing to use herself as a poison bomb like Shinobu did in canon.

Yoriichi after coming to terms with his brother's death ambled over and I could see some wounds upon his soul's body and they weren't bleeding red, instead it was leaking a silver liquid and he seemed to be less solid than before I filled him up with mana when I summoned him.

"Don't bother Jake... After this battle I will not be able to go with you nor do I desire to leave the side of my dear Uta and our children." Yoriichi cut me off as I started pushing some of the leftover mana I had left even as my head tolled like a bell at coming closer to mind down.

"I am an old man, and I simply answered your call to settle old accounts." He said and then I felt the tenuous connection between us shatter as Yoriichi glowed with a silver light.

"I do not merely breathe the sun's glory... I am the suns light." Yoriichi said solemnly and before Muzan could throw him away with his melting titan form's arm the greatest demon slayer to walk this world sprinted forward and over his arm covered in a silver glow with what looked to be a wing on his side and said wing glided through the melting flesh of Muzan's neck like it wasn't even there.

'Yoriichi literally just burnt away his soul to do that.' I thought sadly as Yoriichi turned toward us after he landed and Muzan's head fell to the ground.

"Jake. I left all my teachings with Tanjiro while you planned this battle so don't leave them behind when you leave this land." He said and I only nodded as he didnt really know me all that well, so it wasn't unexpected for him to want to tie me further to the family he once gifted the sun breathing art to.

"I am not fucking dead yet Yoriichi Tsugikuni!" Muzan yelled out and we all looked as Muzan in his human form exhaustedly crawled out of the large head that fell to the ground as the rest of large form was melting away.

I not wanting to ruin the moment, flash stepped behind the exhausted demon with the last of mana and with a powerful down swing of my sword I removed Muzan's head from his shoulder and then punted it away as his body attempted to franticly reach for it.

"No! You are cheating! I was supposed to be immortal! This world was mine!" He cried out and Muzan didnt die screaming as he killed the majority of the Hashira... No, he died whimpering like a bitch as all his forces were slaughtered by the humans he despised as his lesser and his own hands.

Within a couple seconds the wretched crying form of Muzan faded way as his head and body dissolved so fast I didnt even have time to stash it into my space ring though it was probably for best as who knows if he had some nonsense to get around my space rings, time being frozen internally.

But even as all the Hashira screamed out in joy and some in tears at the losses the battle has taken with both Obanai, Sanemi, and his brother Genya dying in the battle my eyes were locked to Yoriichi who gently waved to me as his soul dispersed into nothingness and I had no idea how his soul was mangled when he ignited it to attack Muzan.

"Just let the old man have his rest, Jake." I said sighing at the waste of not bringing him into my Familia as he very firmly told me that he didnt want his wife Uta's eternal rest to be disturbed and was very noncommittal about coming back to my world.

Shinobu and Mitsuri slammed into me for a hug and even if the rest of the Hashira grumbled and if Rengoku had to drag Giyu into it we all shared a celebratory hug before collapsing to the ground in unison from exhaustion.

"Anyone hurt or lost any limbs..." I said tiredly and yes basically all the Hashira had several broken bones, so I passed out the elixir's I had but thankfully no one had lost any limbs as me and Yoriichi kept Muzan and Kokushibo occupied allowing the Hashira to double team the other Upper Moons with me killing Gyokko, Nakime and several dozen weaker demons.

Mitsuri the love pillar just pushed her face into my shoulder as we all laid onto the ground, and I could feel her tears falling onto my shirt as I had taken off my armor when they went to hug me.

"Jake, can you break back Obanai and Sanemi." She asked wetly as she cried at the loss of her friends.

"Yes, just let me rest for a bit Mitsuri." I said gently and patted her head and then I closed my eyes confident Tamayo wasn't going to do anything stupid and the horde of lower ranked demon slayers were cleaning up the battlefield as well.