Asia is attacked by a monster which stole her undergarments as the Occult Research Club arrives to rescue her. Facing trouble to fight that monster due to Asia's request, they managed to destroy that monster with the help of the timely arrival of Irina. Rias then receives a message from Yuuto telling them that Gasper has found the source of the magic. As they arrive to the source of the magic, the Occult Research Club and Irina decides to split into two groups with Akeno and Asia staying behind. The advanced group then encounters the individual responsible for the monsters as he reveals his past story with Issei being in awed with him. Azazel suddenly appears and reveal that the priest who has been stealing women undergarments is the man closest to achieving the Philosopher Stone. Preparing for another spell, the priest halted half way due to the lack of perversion as Koneko reveals Gasper's panties causing the spell to go wrong as the priest became an underwear monster. The underwear monster starts to gain advantage by stripping the girls and manipulating their bras. After having the girls surrounding Ise, the underwear monster, now jealous decides to absorb the girls instead. Issei having determine that the priest is mistaken starts a preach about breasts causing the underwear monster to be in doubt. With Azazel's advice, Issei defeats the underwear monster using Dress Break and the priest is captured. Before leaving, the priest leaves the stolen undergarments to Issei, as Rias and the others decides to leave returning the undergarments to Issei.

[Source: Wikipedia]