Rikako was the only meganekko (眼鏡っ娘, girl with glasses) in the series (but not the only character, as Rinnosuke is a guy who wears glasses). However the Extra Boss of Ten Desires also wears glasses.
Rikako has the longest boss theme in the series, with the music not looping until 4:57.
Rikako's player sprite seems to indicate that she is a normal human and flies by using strap-on rockets.
Morgan, from the Seihou Project, shares some similarities with Rikako.
Rikako being regarded as a heretic by Reimu, the only religious figure back in the time when PoDD came out, could refer to the long time of obscurantism where religion dominated science in most of the world.