User blog comment:B214/Talk About What You Want! 3/@comment-16281343-20150422234027/@comment-16281343-20150427150537

Finally found it. I left out a detail in the short story as I can't remember where it was mentioned but I stumbled upon it when rereading the whole series.


 * Issei said that Rias stubbornly rejected the idea of coming into her room when they previously went to the Underworld. They now know the reason is that it's because of all the junk she collected.

That previous time was in Volume 5: