hashirama didnt do it all alone he needed minato n hiruzen too ...manga hasn't shown any specific technique which can only be used by senju clan whereras evry uchiha can use katon n hence its uchiha's technique ...senju's are said to possess
huge life force thats all ...how to use such life force depends upon user ..lik hashirama's mokuton n tobirama's suiton ...as for four red suns its highly unlikely that its a senju clan technq since hiruzen n minato also provided support to accomplish it
Hashirama needed the other Kages because it requires other Kages to do it.. But Hashirama is the one leading it. Senju clan is the clan of thousand skills. Bringer of Darkness = Senju, The gates Orochimaru used against Naruto = Senju, Kage bunshin = Senju, FTG first used by a Senju, Katon is also used by the Sarutobi clan o-o.
Breakdown of the clans :
Uzumaki = Fuinjutsu
Uchiha = Sharingan based
Senju = Fuinjutsu, Ninjutsu, Genjutsu, Taijutsu....
Senju was a more "all-around" clan then any other clan. Hence why they ended up being superior. I mean a Senju was known for her genjutsu prowess around the world not a Uchiha during Madara's time.
I was under the impression all techniques in the Leaf came from the Senju.
Orochimaru sure did use the Senju technique of the Gates. =x. He probably knows them. What'd be weird is if the animal summonings were from the Senju also. X_X