The word for ascension (of Jesus Christ) in the Japanese version of the Bible is 昇天(しょうてん). However, the verb form 昇天する apparently also means "to die" and "to reach orgasm"...
It seems that many Japanese simply use the katakana word アセンション, sometimes loosely translated as 次元上昇 (じげんじょうしょう ascension to a different dimension)...
I would be curious to see what native speakers have to say on this topic!