User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-176.92.243.100-20150531190948/@comment-75.71.34.254-20150601003145

Actually Ishibumi (aka: "the writers") has done an excellent job of continuity. Ishibumi either has already or will eventually tie together the threads that he begins, drops and resumes. Sometimes there is a significant gap, like not finding out the details of how Issei used Gasper's time stop ability when in Juggernaut drive, until several volumes later.

(BTW: I still think Ishibumi will resolve the apparent conflict of Issei using Dress Break after receiving a new body but before being re-reincarnated by getting his EPs back.)

So chill, Ishibumi has addressed this particular point on his blog (at least I read that he did on a baka-tsuki forum) and has hinted about the problems of putting these cheat-level Hindu Gods in a meaningful context in the afterwords. So I believe that introducing Shiva here was just a prelude to the Shiva arc that would finish the series and Ishibumi will finalize the most powerful lists kept by the different factions as he fleshes out the final cast of characters and their abilities.