Upon reading it another time, I think that Tobirama gets upset when he hears Sasuke talking about destroying Konoha. It is unclear as to whether the 2nd Hokage raise his chakra level or only get emotionally upset, but it seems to scare or at least surprise Sasuke, Oro, Taka and the 3rd Hokage...
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I myself believe that Tobirama must have raise his chakra level to some degree or else why would they seem so scare or surprise at him raising one of his finger ?
The 1st Hokage then rile or rouse his enormous chakra which cause Suigetsu to shit in his pant and cause the 2nd to back down in an instant.