Nagato used a technique that required a lot of chakra in order to summon the King of Hell and execute the jutsu; and Nagato had already used a LOT of chakra and still had enough to bring back everyone. dude, that's a lot of chakra. the jutsu was entirely fueled by Nagato.
the thing is the only Senju we know so far with incredible chakra reserves is Hashirama. whereas we know more Uzumakis with significant chakra reserves. what the manga has stated about the Senju chakra is that it allows a non-Uchiha to better use the sharingan. following this logic an Uchiha who already has the kind of chakra to use the sharingan with Senju DNA can progress even further.
imo this has to do with the whole vitality of the second son topic. which seems similar to the concept of qi (life energy/force). probably the idea is that the Senjus have a lot of raw energy. chakra are the centers from which one can draw this life energy from. which i assume would mean, in the Narutoverse, that when sb is said to have amazing chakra reserves it actually means that they have a great capacity to access those centers and draw more and better quality energy out more efficiently.
regarding the Uzumakis, imho, they have both a lot of qi and chakra= they have a lot of energy and can easily access it and use it via jutsus.
the Senjus probably have a lot of raw life energy and some, like Hashirama, could make great use o it. but Hashirama was one of a kind.
the Uchihas can have a lot of qi (ie Sasuke, Madara) or not (Itachi) but they can access whatever life energy they have easier and make good use of it via their dojutsu.
the thing is the only Senju we know so far with incredible chakra reserves is Hashirama. whereas we know more Uzumakis with significant chakra reserves. what the manga has stated about the Senju chakra is that it allows a non-Uchiha to better use the sharingan. following this logic an Uchiha who already has the kind of chakra to use the sharingan with Senju DNA can progress even further.
imo this has to do with the whole vitality of the second son topic. which seems similar to the concept of qi (life energy/force). probably the idea is that the Senjus have a lot of raw energy. chakra are the centers from which one can draw this life energy from. which i assume would mean, in the Narutoverse, that when sb is said to have amazing chakra reserves it actually means that they have a great capacity to access those centers and draw more and better quality energy out more efficiently.
regarding the Uzumakis, imho, they have both a lot of qi and chakra= they have a lot of energy and can easily access it and use it via jutsus.
the Senjus probably have a lot of raw life energy and some, like Hashirama, could make great use o it. but Hashirama was one of a kind.
the Uchihas can have a lot of qi (ie Sasuke, Madara) or not (Itachi) but they can access whatever life energy they have easier and make good use of it via their dojutsu.
