Even though UTV Ignition hasn’t announced a Western release date yet, El Shaddai: Ascension of the Metatron has shown up on the Japanese XBLM and PSN. This means that if you happen to have either an Xbox Live account that is registered in Japan that you will be able to download the demo up until April 20th, but you will have to have a Gold account to do so.
The simplest way to get a hold of the demo however is to simply make a Japanese PSN account and download the demo at your own leisure for free. Of course if this demo is anything like the Catherine demo on the PSN then you must act quickly because the demo will only be available for a limited time. Also it is worth mentioning, albeit expected, that the demo will be in Japanese.