DNA2 (actually, DNA "squared", not "two") is about high school student
Junta Momonari, and an agent sent from the future, Karin Aoi.  What happens
is that in the future, there is this great overpopulation problem caused
by someone called the "Mega-Playboy" who seems to be irresistible to
women.  He fathered one hundred children through one hundred women, and
each male became a Mega-Playboy, who fathered more children and so forth.
Karin was sent to stop it from the start by shooting Junta with a special
bullet which was supposed to stop him from becoming the Mega-Playboy.
Unfortunately, she brought the wrong bullet, and it was actually SHE
who turned him into the Mega-Playboy, because before he was shot, Junta
actually had a strange "allergy" to girls.  If he saw a girl in anything
sexually explicit, he vomited.  
    So, Karin has the job of turning him back.  Since his DNA hadn't 
stabilized (Mendel had nothing on this storyline), he would sporadically
change back and forth between the Mega-Playboy and his normal, old self.
Karin attempts several times in the first few episodes to change him back,
but she apparently was affected by the Mega-Playboy's charms and actually
fainted after seeing him.  She attempts to reason with him and Junta 
actually falls for her.  Since women couldn't resist Junta, he has girls
swooning over him all over the place, including Tomoko Saeki, whose ex-
boyfriend Ryuji Sugashita, who attempts to destroy Junta after that.  
Junta's, Ami Kurimoto, gets involved.  She, coincidentally, is not affected
by the Mega-Playboy, and Junta is not affected by her either.  What happens
next is a series of misadventures that they all must go through.
    Well, this is one funny story.  Especially in the opening scenes where
Junta is throwing up everywhere.  It's totally unrealistic in the terms of
the genetics they're throwing around, but pretty funny.  The Mega-Playboy, 
incidentally can fight extremely well... and I like those fight scenes...
he has that Ryu-like coolness.  Well, I highly recommend this anime, so
go see it!!