"God of Shinobi" because of how powerful he was especially around the time he was alive.
Hashirama was born during Warring States Period, a time where the Senju Clan and Uchiha Clan were at war with each other; meaning he grew up during this time. During this period, he met Madara Uchiha. As kids, they were always hanging out together and doing friendly-rivalry stuff like skipping stones. Meanwhile, during the fighting stuff, Hashirama did not approve of children being sent to fight and die. He also believed because of that, more bitterness while come between the two clans and cause more people dying. Later, he and Madara found out they were from their rival clans, leading to a fight between the two families since both were spying on the two of them due to suspicion. This clan thing led them to hating each other.
After the deaths of two of their brothers, Itama and Kawarama, he and Tobirama decided that they needed a new shinobi system of childrens' deaths. This also meant an alliance between the Senju and Uchiha, which Hashirama ended up doing the years after on. During this time, Konohagakure was established. Then he and Madara found out they were from their rival clans, leading to a fight between the two families since both were spying on the two of them due to suspicion. This clan thing led them to hating each other.He and Madara found out they were from their rival clans, leading to a fight between the two families since both were spying on the two of them due to suspicion. This clan thing led them to hating each other. He and Madara found out they were from their rival clans, leading to a fight between the two families since both were spying on the two of them due to suspicion. This clan thing led them to hating each other. the alliance thing happened and no more children deaths! I don't know if the alliance lasted until after his death but it probably got taken off when his brother got into office, but we are talking about that later, soo.. Konoha needed a leader! It was Hashirama's wish that Madara would be the leader of the fresh-new village, even though he did a lot of the village infrastructure with his Wood Style. Madara thought Tobirama would either way become the Hokage and abandoned the village. He left the village because Tobirama hates Uchihas. He's an Uchiha, meaning this would be bad for his people. Because of this, Hashirama ended up being the leader. Now called Hokage.
Since Madara left, this meant that Hashirama and Madara are going to fight, again. Which did happen since Madara attacked Konoha a few times, leading Hashirama to fight him. Aftermany many fights with the Nine-Tails aka Kurama under Madara's control, they made one FINAL battle. Hashirama spent some of the battle trying to reason with Madara (which I don't know HOW he can do that without dying. He's that powerful, I guess) and since that battle made the landscape into ruins-like, it was called the "Valley of the End". Madara fought until he was too tired to use his Sharingan. Making Hashirama win with his Wood Style techniques. Before dying-Madara dies, he tells Hashirama how he had changed since the were kids.
After that intense battle, Tobirama hid Madara's body and Hashirama's wife (Wait, WHEN DID THAT GET THERE? WHAT HAVE YOU BEEN DOIN GIN YOUR LOVE LIFE, HASHI?) became the first jinchuuriki of the Nine-Tails. Hashirama helped his brother train the 3rd Hokage, Hiruzen Sarutobi and he had a granddaughter (Hashi, we didn't know you had kids) who is actually the 5th Hokage, Tsunade Senju. Locked away the Scroll of Seals, the kinjutsu inside wasn't useful anymore. This peace didn't last long. the 1st Shinobi World War broke out and Hashirama wanted to make a lasting peace between the villages. Although, that didn't happen! Before he died (We don't know HOW he died), he gave the title of Hokage to his brother and that's how Tobirama became Hokage, guys!
Since he's called the "God of Shinobi", of course he would be very strong. The fields he's very good at are Chakra Powess and Life Force, Ninjutsu, Nature Transformation and Senjutsu.
Chakra Powess & Life Force Edit
Hashirama's chakra was remarkably strong, and so dense that it could visibly affect his surroundings when released. During the Fourth Shinobi World War, after seeing Naruto Uzumaki distribute his and the Nine-Tails' chakra to the entire Allied Shinobi Forces, Hashirama's clone claimed that the distributed chakra had almost as much chakra as himself. His chakra control is advanced enough to perform various complex and large-scale techniques with only a few to no hand seals at all. He was also able to produce ten wood clones while maintaining a Kage-level barrier. (Narutopedia)
His life force can actually make him have enough stamina to fight for 24 hours non-stop while still have left prime to battle. (I can barely do that D: 1 lap and i'm dead) His body is filled with vitality, this also makes him have regeneration powers that are similar to Naruto's regeneration or Tsunade's regeneration.
Because he's a Senju, he's trained in many kinds of shinobi skills. He could use barrier ninjutsu that is very advanced to the point that it could subdue the Ten Tails and you know how strong Ten Tails is! He also knows medical ninjutsu since he can heal wounds without doing hand seals. He can also do fuinjutsu which explain show he could store different kinds of weapons for battle. Lastly, he has shown skill in bukijutsu, which is how he can fight par with Madara, afterall.
Nature Transformation Edit
He can do the five basic nature transformations and can also do Yin Release and Yang Release. Although, he was most popular for his Wood Release. His Wood Release can make wood structures and plants from the ground in many many sizes. This ability is only exclusive to him and only he is known to have naturally have the ability itself.
Hashirama could completely change the landscape with his constructs. He also had more ingenious usages such as making wood clones that are nearly indistinguishable from himself. He could make flowering trees whose pollen rendered opponents unconscious, protective structures able to withstand Tailed Beast Balls, giant hands to apprehend large targets, as well as a giant humanoid creature able to clash with Madara's Complete Body — Susanoo. In the anime, his precision and dexterity with his Wood Release could wield and launch his various weapons from afar, allowing him to attack from multiple angles. When Hashirama enters Sage Mode, his Wood Release techniques become considerably larger and more dangerous, as seen with his largest creation, the Sage Art Wood Release: True Several Thousand Hands: by using it to deliver an enormous barrage of punches, it could strip Susanoo from the Nine-Tails plus was chiefly responsible for the formation of the Valley of the End. (Narutopedia)
His Wood Release can also make him be able to capture tailed beasts. He uses this technique that is too long that I don't want to add, but the technique he used makes the tailed beast falls asleep. He used this method on many tailed beasts and has taken control of them all at the same time. He can also make wood dragons that can wrap around someone and absorb their Chakra.
Can someone do this along with Senjutsu, please? I am tired.. Thanks in advance? -Supoz