Most of the first 40 minutes are battle scenes, but are "cutesy" and designed to set up an alarmingly happy setup early in the film to show the viewers that something is not right.
A character (in a metaphorical transformation sequence, as in it technically doesn't *actually* happen) stabs her chest and her heart is briefly seen on the end of her sword amidst the blood-spray if one pays attention. This is a very very short shot which is shown as a silhouette, and is very downplayed and not at all intense.