Originally, his name was The Phantom. Then they settled on Akira Kurusu, which if I recall, was a series of play on words that fit the character very well (It was along the lines of "The Protagonist", something of how the Kanji is arranged, as a placeholder name).
They eventually settled on Ren for the sake of the Anime and Dancing game, as the name Ren Amamiya is another play on words meaning Lotus and Palace (or literally: Raining on a Palace, in terms of destroying/purifying), but with an extremely effeminate tone to the name, it does not, and never will, resonate with me.
(edited by Joker)