Saruyama Kenichi

Kenichi Saruyama is the perverted best friend and school mate of Rito. He has known him since junior high and is more open and obvious of his obsession with girls and is one of the few male characters Rito can talk to about his situations involving Haruna or Lala. He is aware of Rito's feelings for Haruna and consistently advises he get together with her. Saruyama reveals that he has a crush on a girl named Yūsaki Riko, but does not realize she is actually Rito, who is accidentally transformed into a girl by one of Lala's bizarre inventions.

Being one of the few significant male characters of the series, Saruyama's role is generally that of a luckless loser who desires but never gets a girl, and an underdog to the more popular male protagonist.

Appearance
Kenichi Saruyama has black eyes and black spiky back hair, most of which is pointing back.

Personality
Saruyama is quite perverted, He would try to peek in to girls hot spring and bring Rito along, and if ever caught he would put all the blame on Rito, he doesn't seem to care about the consequences about his perverted actions. He can be really jealous of Rito (along with almost all the boys in the school) because how close he is with a lot of pretty and popular girls. In the first chapter, it is also shown that he has bikini model posters and magazines in his bedroom, further cementing his perversity.

He currently has a crush on a girl named Riko Yuusaki, who unknown to him is actually Rito transformed into a girl by Lala's inventions. Sometimes he would imagine being in romantic (or ecchi) situation with her, which Rito understandably finds disturbing. Saruyama is no less a pervert and a loser around "Riko" as he is any other time when he talks about girls, which disgusts Rito.

Plot
In the original series, Saruyama would appear casually, almost never without Rito around. He would mostly a hang out with Rito, going on beach trips or to swimming pools with others of the main cast, sometimes he would give Rito chances for him to be alone with Haruna (although he would also try to get in perverted situations with her and other girls) and talk to Rito about how great breasts are. Saruyama would never miss a chance to peak on girls bath and would bring Rito along and make him take the blame if ever caught. Every now and then, he would feel jealous of how close Rito is towards girls.

In To Love-Ru Darkness, Saruyama appears less frequent and continues to be angry and jealous of Rito because of how close he is to all the pretty girls and getting in good/ecchi situations. He also joins the Principal as they chase after girls often; whenever either of them try to do so, it doesn't seem end well. He still has a crush on "Riko".

Yūki Rito
His most notable relationship is his best friend Rito. The two have known each other for a long time and he is the closest male friend Rito has. Saruyama seems to understand Rito's shyness and clumsiness around girls almost better than anyone else. He wasn't at all surprised when Rito failed again to confess his love to Haruna. Saruyama has made some attempts to help Rito get together with Haruna. He also noticed how much Rito has changed around women since he started hanging with Lala.

Although they are friends, they both have certain dislikes towards each other. Rito doesn't like how other students see them grouped together when Saruyama starts acting and talking like a pervert. Saruyama envies Rito for being close to Lala and many other girls, even though he already has feelings for Haruna. Still, the two are on good terms on some occasions.

Saruyama is unaware that Rito is actually "Riko", the girl he has a crush on.

Lala Satalin Deviluke
In the original manga, Lala sometimes helped Saruyama out, such as when he wanted to go on a date with "Riko". The two are friends through Rito, though they aren't particularly close and he is one of the few people besides teachers that Lala is on a last name basis with. Saruyama finds Lala highly attractive, due to her big boobs, though he also finds her shrunk down form cute. This likely explains how he uses the "-chan" honorific when referring to her.

Sairenji Haruna
Saruyama isn't exactly close with Haruna and she hates it when he makes perverted comments, although the two are still friends. Sometimes Saruyama would try to get Rito alone with Haruna so he can confess his feelings to her, but he would also try to get into an ecchi moment with her (as he does with most girls) which fails in the end.

Trivia

 * "Saruyama" (猿山) literally means "monkey mountain", referring more to his perverted nature.
 * The only female that's ever loved Saruyama was an unnamed cat-like woman alien in the anime who saw him as a perfect father for her child.
 * Interestingly, there are no characters who address him by his first name; not even Rito or Lala do this.