In the future, Earth has a major problem: over-population. To combat this threat, nobody is allowed to have more than one child. However, this isn't a permanent solution, so scientists have searched long and hard for the root of the issue, and in the end, they found it: Junta Momonari, a mega playboy who, in his time, impregnated one hundred women! And so, Karin Aoi, a DNA operator, is sent back to the past to inject Junta with new DNA that should solve the problem once and for all... there's just one problem: Junta has a serious allergy to girls and throws up whenever he sees them! Regardless of Junta's lack of symptoms, Karin must carry out her mission; and that's where things start to get interesting...
In both stories, a girl/woman from the future goes back in time to alter a tragic future/future event by changing the DNA of a certain guy in the past. Things might turn out quite different than they intended though.
Both series are about a girl/woman from the future who travels back in time to stop a sex-obsessed guy who wreaks havok in the future. Strangely, the version of the guy that the girls encounter is the exact opposite of what history says. In both cases, the reader is left wondering if history made a mistake, if the time travellers wind up causing the very events they were trying to prevent, or if something else is going on.
Yuuto Amakawa has had a tough life. Seven years ago, both of his parents were tragically killed in a car accident, leaving him without a single living relative. His friend Rinko Kuzaki has taken care of him every since. Yuuto's sixteenth birthday has arrived, but instead of a birthday gift of a normal life he meets Himari, a catgirl samurai who swears to protect him. Within weeks Yuuto's life is thrown into chaos as his family's dark past comes to light. With demons appearing around him, Rinko and Himari fighting for his attention and a sinister plot beginning to surface, can Yuuto live the normal, safe life he wants so badly?
DNA squared and Omamori Himari are two strikingly similar series. Both about a more-or-less average boy suddenly discovering he has powers, and both about him gaining popularity and girls because of it. On top of that, both are fairly fanservice heavy.
However, the Art is vastly differant between the two and Himari has a much deeper plot then DNA.
Rito was just an ordinary high school student, but that changed the day an alien princess named Lala appeared in his bath tub. Before he knows it, he's engaged to the most important woman in the universe and her jealous suitors are trying to kill him! When Lala decides to enroll at his school, Rito has to survive both attempts on his life and Lala's crazy inventions, and somehow find the time to confess to his real true love, Haruna.
Both these series are, really, shameless Ecchi. While DNA has more Harem aspects and To Love-Ru has more comedy aspects, both boil down to the same equasion. It is fairly likely if oyu like one youll like the other.