Why does Hashirama Senju possess such huge and terrifying chakra?


In the past three Naruto manga chapters (chapters 621~623), the story goes
like this: child days of both Hashirama and Madara, and he (Hashirama) is just
like every others in Naruto: a normal human being. But when Orochimaru revived
all four Hokage in front of Sasuke, Hashirama raises his chakra level to
threaten Tobirama, as it would crack all the walls nearby or maybe the entire
basement (chapter 620). How could have Hashirama acquired this kind of power
(chakra)?




When Naruto had gone to Mount Myoboku for his senjutsu training, Lord Fukasaku
had mentioned

> only those who already possess "extreme chakra levels" can utilise natural
> energy to invoke senjutsu

[Source](http://naruto.wikia.com/wiki/Sage_Mode)

Now we also know, Kakashi mentioned Naruto having large reserves of chakra
(excluding the Nine tail's chakra). And this is the reason why Naruto could
complete the Sage training and enter Sage mode, thereby giving him access to a
larger amount of chakra.

The same goes for Jiraya, as he had completed the Sage mode training, and
could enter the sage mode himself.

Thus we can assume, once in a while kids are born with higher reserves of
chakra.

The same can be assumed in case of the first Hokage and Kisame, they could
have been born with a large reserve of chakra.

Reason for assuming this is, First Hokage could enter the sage mode himself,
and as for Kisame, we know the sword of his, Samehada would only attach
himself to a ninja with good reserves of chakra. (Since the eight tails had
more chakra and a more "delicious" one samehada switched allegiance and joined
Bee).

In case of Naruto, Jiraya and First Hokage, their sage mode gave them access
to a larger pool of chakra thus making them more powerful. On the other hand,
Kisame could get access to a larger amount of chakra with the help of
Samehada, that would "eat" the chakra of enemies and supply to Kisame.

Nothing much have been mentioned about the third Raikage, so I can't provide
any proof to support my speculations.

