LE is activated by having a bard song active on the wielder.. Definitely useful for those incredibly rare situations where there is a bard in the party and the ninja is expected to tank <.<;;
Just to make it clear, it can pop in any of the 8 small rooms on the 1st map. 6 of the rooms are on the map, 2 are hidden. The doors must be opened, they are caled Granite doors if I can recall. It pops every 2 hours in one of them. Just click on it can you'll get the rattle.
(Cuz i've been there twice now and haven't been sure how to get it ;) , hope this can help someone.)