Trinity Seven is a typical Japanese style fantasy manga. It has all of the hallmarks of such a story. This includes the fan service, the domineering guy (who is also lecherous, by the by), the girls who just need to be shown kindness, the tsundere girls that abuse him, so on.
Of course, the guy, Arata (our main male protagonist) is really powerful. But in this case, so are the girls. It isn't that this never happens in such stories, but usually the powers of the ladies aren't focused on as much. The girls here are, in some ways more powerful than Arata, starting with Lillith-Sensei.
The story starts when Arata notices strange things happening, like his cousin/childhood friend acting strangely and the sun being black. He pushes the issue and finds out that the area he lives in is no longer around. It was subjected to something called a "breakdown phenomenon". This occurs when magic goes out of control and the surrounding area is destroyed. Apparently, this happened in Arata's town and he recreated it through (unknowing?) possession of a special magical grimoire.
Unfortunately, this could cause future disastrous problems, so Lilkith (who tracked him down when investigating the breakdown phenomenon) gives Arata the choice to have his memory erased or be killed. But when he finds out his cousin, Hijiri, still lives and could be restored, he rejects this and asks to be trained at the magical academy where she teaches instead. This way, he can eventually bring Hijiri back.
The story is fun, and quite humorous. It us somewhat sexist in the "women are emotive, men logical" department. Though this is only a plot point to explain why the most oowerful mages - other than (the impulsive, emotive Arata - are women. And the "toilet humor" might bother some, but it is relatively minor, to be fair. The art is detailed and good, this being a big fan-servicey series and all. Characterization, other than Arata being a major siscon, Lillith a lonely and uptight teenage prodigy, and some other characters being mischievous or weird, is not big. Of course, this is the first volume.
I quite enjoyed and recommend this.