[Rei-Tenshi]

Originally Posted by chronotrig

Spoiler for the 'answer' track:

It's first played in ep2 when Battler and Beato's game starts up. (chapter 4)
Then it comes up in ep3 when the meta world reaches the first twilight. (chapter 9)
...Apparently, it also used to play at the very, very end of the latest translation patch, but Ryuukishi commented it out.

And it does play three times in ep4, if you're interested.

Ahh, thank you.