Maken-Ki is an anime that has almost no plot...or so everyone has said. This is not exactly correct in the truest sense, but the plot has been so underdeveloped for the sake of having so much fanservice that the plot feels practically non-existent.
The basic plot is this: "Takeru Oyhama has enrolled at Tenbi Academy, a high school that converted from all-girls to co-ed. Hoping to have a life full of ogling pretty girls, he reunites with childhood friend Haruko Amaya, who shows him around school. However, he learns that the school is for students who possess magical and spiritual energies called Elements and who wield crafted weapons known as Makens. The students engage in school sanctioned combat matches that showcase their powers. While his own ability and Maken is not apparent at first, Takeru soon finds himself surrounded by girls, including Inaho Kushiya, an attractive girl who says she's his fiancée, and Kodama Himegami, a popular blonde who says she wants to kill him. He joins the Security Committee, also known as Maken-ki, which supports the student council's operations."
This plot reads exactly like every other Harem-genre anime out there, from the random guy who ends up in an all girls academy where something unusual (magical girls, battling robots, etc. etc) happen, to the the guy ending up with several girls who seem to be attracted to him for no discernible reason (Childhood friends, promise made over a decade ago, they kissed when she randomly fell on top of him). Even the humor is terrible, not just cliche'd but understated in such a way that it's simply not funny.
It this lack of originality in plot more than anything that ruined Maken-Ki for me.
Let us take the main protagonist as our example of what's wrong with Maken Ki. Takeru Ohyama is, in all regards, plain. He is exactly like every other harem protagonist out there: perverted, idiotic, a complete loser with zero intelligence and no talent except for one ability he can't even control....oh, and he seems protective of his friends. Sound like someone you know? How about several someones? This guy right here personifies what it means to be the progatonist of a harem anime. An idiot no girl would look at twice who somehow makes several girls fall in love with him for no discernible reason.
Not only is the plot underdeveloped, being nothing but a thin smokescreen for ecchi fanservice, but the character development is stagnant. None of the characters ever evolve, they never change. In fact, everything remains the same in this story. Even at the end there is no real difference from when the series started. Just about the only good thing this series has is the ecchi fanservice.
This anime gets a 4/10 in my rating. And the only reason I'm even giving it one that high is because the ecchi allowed me to force my way through to the end.