My appreciation for this side story is influenced by my seeing the theatrical movie, which was also a side story. This ONA and the movie have similar plots points, sickly female royal cursed by a shady court physician and a brotherly rivalry, stands out the most. However, my choice would be this three-episode ONA. It just has better pacing and tighter plotting, without the need to cast cameos from other series regulars who do not have a major role in the story and thus making for a clunky and overdone mess. For Tensura fans, this is something to tide you over waiting for the next full seasonof the main story. Don't expect too much and enjoy the show.