Before deciding on consuming Hashirama's clone, Chiba had days after the poison incident to learn two scrolls that he copied from the Akimichi clan.
In the one piece anime, It was show that users of the Life Return technique could instantly digest food. This realization made Chiba instantly gravitate towards the Akimichi clan as he remembered a powerful jutsu that they had that regarded weight!
The first scroll he had copied was the heavily guarded recipe for the Akimichis three colored pills! The first green pill grants user increased strength in exchange for intense muscle pain, the second yellow one increases users strength even further and leaves user completely immobile and in agonizing pain afterwards and the last Red pill converts all of the users fat into chakra, supposedly killing them afterwards.
Chiba only needed the Red Chili Pill for his plan to work, thankfully this pill was the easiest of the three to make.
Making these pills required specific ingredients that could only be found from around the world, thankfully the Akimichi clan had these ingredients in their storage room and Chiba didn't hesitate on taking all of them with his Devil fruit before Orochimaru or Danzo could.
The other scroll was a Jutsu worked in conjuncture with the Red Chili pill, Butterfly mode! This complicated jutsu would focus the chakra from the fat to chakra conversion, allowing the user to actually use this abundance of chakra instead of just internally exploding from chakra overload.m!
While this jutsu just focused the abundance of chakra into a battleform, with enough training the user could actually induce it without pills or side affects! Doing so would take years of intense training and required the user to constantly be fat, so Chiba never planned on using the Red Chili pill in combat.
So using the equipment he had stolen from Orochimaru, Chiba began concocting the third pill from the instructions. This would normally be an incredibly difficult thing to achieve for a first timer, but Orochimaru's highly advanced equipment and Chiba's observation Haki which helped predict failures in the future greatly helped Chiba make the pill.
It was only after learning those scrolls and making the Red colored pill that Chiba had consumed the Hashirama clone, and he was glad he had prepared for it.
Despite feeling much stronger from the blood and consumption of the clone, Chiba didn't want to spend over a month of intense training just to lose the weight, especially since hed be constantly reminded of the terrible act that he had done.
Although Chiba had killed Dozens to over a hundred people during the war, it was the act of consuming Hashirama's clone that revolted him to his very core. Despite him not actually doing anything evil since the clone was already dead, Chiba felt like he had crossed a line and internally wondered if this was the right move.
Shaking off those thoughts, Chiba mentally prepared his mind for the pain he was about to endure as he planned on using up all of the chakra he obtained from the fat for just a second!
With hus life return ability he could affect the rate at which his body digest things, so looking down at the red pill in hand, Chiba didnt hesitate for a second as he bit down and swallowed it!
Gritting his teeth, wings akin to that of a butterfly suddenly appeared on his back as the fat on his body started disappearing at an alarming rate! Without hold back, Chiba activated his observation haki to it's absolutely max as he saw everything within two thousand miles from him in all directions!
He saw dozens of buried tombs with vast treasure, animals that were size of skyscrapers, evidence of previous civilizations but eventually he found what he was really after. Searching pass the thousands of white zetsu that were scattered throughout the entirety of his Haki's sight, he saw that located in a deep cave hidden in a mountain was a humanoid creature that was completely black like the void, he saw the black zetsu!
'If I can kill that black zetsu, then this world is safe from kaguya's threat!'
The moment Chiba saw the black zetsu, the black humanoid opened it's eyes as it seemed to peer back at Chiba!
Immediately shutting off his observation Haki before the zetsu could find out where he was, Chiba crumpled to the ground. The once incredibly obese and rotund Chiba was now emaciated and rail thin!
His body was steaming and his lips were crusty like he hadnt drank in days! Struggling to stand up, he slowly walked to the fridge as he used the walls to help him.
'If I had attempted butterfly mode before obtaining the Hashirama cells and became fat, i'd definitely have died!' Chiba knew that if someone had poisoned him with that red Chili Pill, he probably would've died before he could fully digest it!
Opening his pantry, Chiba took out a dozen ramen noodles cups and ate all twelve of the hard noodles without wasting time with water and activating his life return ability.
In the span of five seconds, the emaciated and bone thin Chiba slowly grew larger as his muscles had gained some definition. He digested the food and absorbed the nutrients nearly instantly and continued his search for food.
Chiba still looked unhealthy thin but not dangerously skinny as he moved onto the food in his fridge, using the D-ranked fire palm jutsu to cook the unseasoned meat, he started scarfing down pounds of meat.
Biting into a medium rare steak, Chiba looked down at the reddish meat and couldnt help but think back to the iron fishy taste of Hashirama's raw flesh. Covering his mouth to prevent himself from vomiting, Chiba cooked the steak until it was well done before eating the rest of it.
'I guess if the only downside from eating Hashirama's body is now i have to cook my steaks well done, then it was an equal trade off.' Chiba attempted to joke about it but was internally absolutely revolted thinking about what hed done.
It was only after eating everything from the fridge and two large bags of uncooked rice that Chiba had returned to his normal physique and he realized just how strong hed had become!
Despite having very little chakra remaining and was weakened thanks to the butterfly mode, Chiba felt like he could take on his previous self with ease!'
Once again using his life return to manually control his body, Chiba's right index finger nail suddenly grew larger and sharper as he raise it to his forearm and slashed, creating a deep cut.
Chiba watched in shock as the deep wound had completely stopped bleeding in thirty seconds even without using his life return!
In another minute the edges of the wound had started closing together as Chiba decided started to use his Life Return to manually heal the wound, not wanting to leave a scar from the natural healing process but became shocked at the results.
In the span of 10 second, the once deep cut had completely disappeared completely with the conjoined effort of life return and Hashirama cells!
'This can actually be used in combat! I don't know about severed limbs, but I can potentially survive any wound so long as I'm conscious and my heart or brain hasn't been damaged!'
The Hashirama cells added a passive healing ability that wasnt as powerful as his life return, but when he mixed both of them together the results were outstanding! Chiba only had to stall a ninja for a minute and he'd be completely healed from whatever damaged he'd sustained!
Besides his now extremely powerful ability to survive nearly any injury, Chiba felt his chakra capacity had now grown to that of a Jonin despite still being a child!
The higher chakra capacity and the added Hashirama's cells also made his body much stronger than before and joined the rank of Jonin as well!
'With this, I'm garaunteed to become a kage level ninja once I reach adult hood but will I survive that long? Danzo now knows that an Uchiha has the ability to sense every person in Konoha, sense secret bases, and has the ability to destroy thousands of different building and levitate humans...'
Chiba knew that someone like Danzo wouldn't allow such a powerful ninja like himself exist if he didn't have complete control over them.
'Whether it's my ability to attack thousands of targets all at once or the fact that he is now paranoid about whether I can sense what he does in the shadows, Danzo can't let me continue unhindered.'
This realization was the sole reason that Chiba let go of his pride and consumed Hashirama, an act so revolting he wouldnt do it a second time if given a chance.
'I need to increase my Fuinjutsu training! Despite having consumed his entire body and got a blood transfusion , It was definitely less affective consuming it than getting a limb transplant! Sealing a powerful animal inside of me is still the way to rival the truly godly people in this world!'