It goes without saying that this title goes way past the 25 character limit. I don't think that using only el-shaddai would be good because it's primarily a biblical term and searches for "El Shaddai" without the subtitle bring up primarly biblical references (and a few songs).
Right now, I'm leaning towards what we did with Space Invaders Infinity Gene and The Wonderful End of the World and tag it as el-shaddai-ascension because el-shaddai-ascension-metatron is still too long.
Though the longest part of the name is a subtitle, as far as I know, there are currently no plans for a sequel, so I don't know if we should treat it the same as how we treat tagging series. I think using el-shaddai-aotm would be a poor decision, seeing as googling for "el shaddai aotm" brings up 4.5 million hits as opposed to "el shaddai ascension" which brings up 9.3 million.