Pailingual

Bilingual is a spell created and used by Issei Hyoudou.

Summary
First used in Volume 5, during the Rating Game between the Peerages of Sona Sitri and Rias Gremory, the spell is a powerful and feared (by women) spell to gain information. It has, since it's introduction, become one of Issei's trademark spells. It has however been banned during Rating Games.

Abilities
Bilingual is an area effect spell that causes women's breasts to speak, revealing their thoughts and plans, allowing Issei and his allies the ability to come up with counters or defenses. This spell is noted to seemingly bypass spells or other defenses against mind reading.

The voices given to women's breasts are not always identical to those of the women, sometimes having characteristics that the women's own voices lack.