Firstly I must state that apparently this manga is based off an otome game. While I have read manga that were also based on otome games they had better depth than this one.
It's dreadful. Many things that occur within this manga are never explained. So on the few moments that things start to get interesting, such as the mad baddie character Yamato's background snippets, it never goes further than a few frames displaying a complex character history. This applies to most of the characters so you never really get to know them beyond the few things they cared to put in for you to read (which isn't a lot).
To summarize what this manga is about in my words, an average high school girl gets sent back in time to save an important historical character by a water spirit.
There isn't any special reason for Mana being select, you could say she just happened to be there and is expected to somehow save a particular person without being told how she is supposed to save them. This leads me into...
The main character girl fulfills the classic otome character. Basically she's a "blank" that a reader can imagine as herself. Mana isn't anything special and is really boring.
The only character's I had any interest in where the ones who were revealed as to having some dark or mysterious past (which as stated earlier are only given glimpses and nothing more, no conversations, no flashbacks, no close-bonding story between characters). All the other character's are just sort of... there.
I do love the quality of the art and the style. This is pretty much what kept me reading... that and the hope that something deeper would occur, such as Yamato's history (which doesn't make much sense with the details we are given).
If you are seeking a nice past era romance manga, I would say to skip this one.