According to Amazon Japan, Toaru Kagaku no Railgun S official visual book will include an original anime video on Blu-ray disc.
The OVA is titled “Daiji na Koto wa Zenbu Sentou ni Osowatta” (All Important Things Have Been Learned in the Hot Bath) and it suggest that it will take place at a hot bath. The visual book and will be released on March 27 at around JPY 3,000.
An earlier OVA, ‘Entenka no Satsuei Model mo Raku Ja Arimasen wa ne’ (Being a Photo Shoot Model Under the Hot Sun Isn’t Easy, Is It?) released in 2010, is a beach episode.