Konoha:

In the most famous building of Konoha, that is the Hokage building an old man was sitting on a chair with load and load of paper and reports on his desk which needed his reviews and signatures, even though he was currently the most powerful and respected person in the whole village, 

But only the feeling of immense sadness and tiredness can be seen on his face, with a smoking pipe in his mouth Hiruzen Sarutobi was staring out of the window at the 4th Hokage monument 

Konoha suffered the most losses of any village in the 3rd Great Ninja War due to having to fight every village. And merely a year later, they had to face another assault from the rampage of the nine-tailed beast which not only killed the 4th Hokage, but also a lot of their ninjas and civilians. 

This not only increased the burden on him and the existing ninjas but also caused Konoha's orphanage to be overpopulated. Hiruzen sighed again, finally starting his day by getting that damned paperwork done.

Normally an orphanage will have fifty to sixty children every year in Konoha, but due to the following incident not only have existing orphanages become full, but many new orphanages have to be opened to meet the demand for orphanage 

In one of such orphanages, Kaida Senju, a 5-year-old orphan was being treated since he got into a fight with some older boys who were badmouthing his parents and sustained a significant head injury.

After being treated by a medical ninja, Kaida Senju woke up with an intense headache, thinking 

'damn, what with this headache, as a patient of "Chronic Regional Pain Syndrome' I am quite familiar with pain throughout all my body but this headache seems different its not some external pain but something else'

Slowly he opened his eyes and looked around. Frowning upon noticing the unfamiliar surroundings 

"What is this? Where am I? This is not the hospital room I am familiar with" With his memories all jumbled up Kaida was confused about everything around his situation when he noticed 

"Why are my hands so small? Wait why am I so much smaller, did I somehow return to the past"

But his train of thought broke when a middle-aged man entered the room he sat beside Kaida and asked "Kaida, how are feeling now"

"Who are you, sir? and why are you calling me Kaida" Feeling more confused Kaida asked the man 

Man replied in a worried voice " Oh! I think the injury has caused some memory loss, do you remember anything Kaida"

After hearing the question Kaida tried to remember more about the name, and that's when his headache intensified and he passed out again, the old man became worried and quickly called the medical ninja again but after inspection ninja said 

"Since he is so young I think the injury on his head has made him lose his memories, there is a chance that they will come back after 1 or 2 weeks or they may never come back, but his physical condition is good so there is no need for you to take tension"

"thank god he is not in some danger, and about memories, it's good that they are lost since he lost both his parents during the tail rampage now he can make some new and happy memories for himself" 

The old man was the caretaker of the orphanage as a retired ninja, he could have lived a simple carefree life but he decided to start this orphanage all by himself since he was just a chunin during his career his assets were not so much, then also he decided to start this orphanage as he was also an orphan and knew how much important a simple shelter is for a child 

As for Kaida he especially cared for this child, Because he was indebted to his parents, they saved his life during the 3rd Great Ninja War 

While Kaida pretended to be asleep, he started to gain access to new memories. Memories of Kaida Senju. It took five hours to gain clarity, an insufferable headache, and disbelief for him to understand, 

'Fuck! I transmigrated! And into the fucking Naruto world of all places! But how? I don't even remember dying. Don't you need to die to transmigrate? 

And damn, transmigrated from that safe world with rules and regulations into this deadly world full of cunning and powerful ninjas. Due to that disease I always wanted a new life but never in my wildest dream have I imagined having this as my new life'

After a few minutes of disbelief and ranting, he finally calmed down and decided to understand and plan his future. He thought, 

'All right, I guess I'll be known as Kaida Senju from now on. Unlucky fellow to lose his life to someone transmigrating into him. I wonder how that even works! 

Anyway, I got a lot of information from his memories. His parents seemed to have died in Kurama's rampage and he was incredibly lucky to live. And damn, after being admitted into the orphanage, he was examined by Root to see if he can be taken in. Lucky me that they didn't choose him. Hmm, since Kurama's attack took place a year ago, and since he is 5 years old, it seems I'm 4 years older than Naruto and his generation. All right, that gives me more time to train and gain power.

The Uchiha massacre should occurred after around 7 years, the Konoha crush after 12 years, the Pain attack, and the 4th great ninja war after 16 years. 

Wait, what's this feeling?' At that moment, he felt a weird energy flowing through him. He thought, 

'Is this chakra? His memories didn't have anything related to chakra. So does it mean that chakra was unlocked when I transmigrated into him? Finally some good news. With this, getting into the ninja academy should be easier than other orphans. However, I wonder how my chakra level compares to the chakra level of others. Anyway, probably better to get a look at the surroundings first to understand more about this place'

 With that, he finally stopped pretending to be asleep and woke up.