Possibly the most beautiful episode of the whole series.
I'm not just talking about aesthetics - but the deep emotion and messages it conveys. Though the animation and direction is by my -most- favorite team (the team changes every episode), this episode was moving for the fact Sango is so close to her brother, yet so far.
I cannot even imagine the hurt and turmoil she has been through, thinking upon the idea that her little and only brother can face death at any moment. Sango believes her brother's heart is still good and she is right ... if only he were only allowed to show her that fact. The part where he is hidden behind the tree as she is mere feet away is deeply saddening.
The most heart-wrenching part is when Sango follows Kirara and is shown the Secret Garden of Lilies - the flowers she was once given by her little brother. It brings a sense of nostalgia, wanting, and despair. She is confronted by the memory of Kohaku bringing those same exact flowers to her, when they were happy.
It's great that though this is a filler episode, it shows that Kirara is as attentive and intelligent as the rest of the characters (as said before by another reviewer). Though everyone brushes her off as the 'pet' of the group, and really pays no mind, it's great to see some insight into what she thinks and remembers.
I never really cared TOO much about the relationship between Sango and Kohaku when I watched this series as a child. But going over this as I'm 6 years older -- this is the one concept of the WHOLE show that can earnestly make me cry.