Takamasa Sougi is known to be the youngest and most talented priest. He is also the Contracted Priest and lover (as the series talks about their past) of Itsuki Yamagami. Itsuki wanted a priest who is the strongest to make contract, so she could enter heaven faster, and the answer was him (a student who is roughly 19 years in age at that time.)
His specialty is archery. With that, he provides support to Itsuki when she is on a killing mode.