User blog comment:B214/Question and Answers 3/@comment-188.119.192.48-20140702010537/@comment-1359322-20140702050343

It was actually taken from Ishibumi's tweet in his tweeter.

Ishibumi originally planned to have Ophis use the last of her power to help in reviving Issei and disappear. But Ishibumi felt that it was too pitiful for Ophis, so he decided to make her a mascot.