High School DxD, Vol. 17 (light novel): Professor Valkyrie

A Rocky Reunion!As Issei and the others hone their skills for the battle ahead, the Hyoudou residence receives a surprise visit from…Rossweisse’s grandmother?! The wizened spell caster, Gondul, commands great respect from her young Valkyrie granddaughter, and Issei is caught unawares when she reveals that one reason for her visit is to meet Rossweisse’s boyfriend! Now who might she be referring to…? And just what is that unsettling aura that seems to cling to her?