In both, the story of Momotaro is remade into something completely different, and both fail to make more interesting story. While Momo Kyun Sword is more fantasy and Momotaro is a girl, Momotarou no Umiwashi is historical and serves more as a propaganda during World War II.
Both are based on Japanese folklore. While Hoozuki no Reitetsu has more combined legends/myths including legend of Momotaro, Momo Kyun Sword is based only on legend of Momotaro. Hoozuki no Reitetsu is more comedy and Momo Kyun Sword has more action.
Both are fantasy anime about a group of big-breasted world that fights enemies. Both have fanservice, but Momo Kyun Sword has more frequent one. Hazuki and Momoko have somehow similar character. Both anime are setted in past.
Both anime has a character who merges with a spirit/gods to defeat their enemy.
Both anime have fansercive with the main girl having big boobs.
Both are fun to watch if you want something that doesn't really have a plot.
Magical girl series whose crystal collecting main plot focuses more on the motivation of the antagonists than why the protagonists are trying to stop them. Fate and Onihime both have similar issues trying to gain the approval of their sole parent.
Both contain quite a bit of fanservice, albeit Momo Kyun Sword is ecchi-centric whereas Lyrical Nanoha doesn't dwell on it.
Fanservice filled action fantasy stories where the female cast tend to lose their clothing during battle in place of being injured. Both have simple stories that, if not for the rampant sexualization, would basically be kids shows.
Where Dog Days focuses entirely on dog/catgirls, the titular character of Momo Kyun Sword fuses with her animal companions. Additionally, Eclair and Momoko have the same voice actress.
In Inuyasha the cast is going around trying to get the shikon jewel shards and in Momo Kyun Sword the cast is going around trying to get peach fragments. Both shows involve needing to stop the demons or others from getting to these fragments first.