As a toddler Tobirama hadn 't understood why the world was so bright, so overwhelming. He hadn 't understood why no one else seemed affected. By the time he was three he understood that he was a sensor and that this was both a blessing and a curse.

True sensors were rare and the Senju clan were blessed to have one born in their midst. Tobirama had the ability to feel chakra in nearly all living things, differentiate them from each other, and assess the strength of each signature. As he grew older he developed the even rarer ability to sense emotions from those chakra signatures if he concentrated hard enough. He was the strongest sensor ever to be born in Fire Country, able to feel a single individual four days travel away.