Momioka Risa

Risa Momioka is Haruna  and Mio 's best friend and Rito 's and Lala 's classmate. She is very fun-loving, mischievous and perverted. She enjoys talking about naughty things, teasing Rito, and her favorite thing to do is groping the breasts of other girls and whisper naughty things to their ears as a means of teasing them.

She is also part of her school's tennis club like Haruna, but she mostly skips it to do other things like karaoke.

Appearance
Risa is an attractive girl with dirty blond colored hair and dark brown eyes. She has a curvaceous figure (though not at the level of Lala or Yui) and seems to have some trouble keeping some men at bay. Of all her classmates she is probably the most willing to use her figure to attract attention, save for comedic scenes.

It's also notable that when in school, she does not wear a tie, which is included and supposedly required with the uniforms of female students.

Personality
Risa is quite an indecent woman, as she always goes around groping other girls breasts and suggesting how something would lead into an erotic situation. She is also enjoys teasing with other people through about sexual things. She is quite nosy about other peoples personal business like their love lives, like when she asked Yui if there is someone she has in mind or giving Lala bad advice about her relationship with Rito.

Rito Yuuki
It is not known what Rito and Risa feel for each other, but it could be assumed that they are generally friends, or at least acquainted through Haruna. While various other girls consider Rito to be a pervert, Risa knows that he is an innocent boy to a fault and likes to tease him about sexual subjects, like grouping a girls breasts in front of him.

Rito wishes that the naive Lala would stop taking lewd ideas from Risa and Mio. And Risa doesn't take Rito's rejection of sex and temptation seriously, and likes to play with his shyness around girls and occasionally gropes the breasts of other girls in front of him, not knowing that she's making him feel truly uncomftorable.

Very early in the story she didn't think much of him as anything special but It has been shown that Risa might have feelings (or at least lusts) for Rito but it hasn't been detailed if she was serious or joking. In chapter 147 and episode 10 of Motto To Love-Ru, she takes a much closer and bolder approach in teasing him, but it is still not clear what her true feelings for him are. She has gone on record that saying he can be helpful, innocent and even cute when he overreacts to things.

Lala Satalin Deviluke
She is good friends with Lala and likes groping her breasts. Risa often gives wrong or lewd ideas to her questions about how to get Rito like her a lot, something he really dislikes about the two.

Mio Sawada
Risa's friend and partner in crime, she also enjoys groping girls' breasts and whispering in their ears.

Haruna Sairenji
Risa's friend, whom she occasionally gropes along with her friend Mio, sometimes saying they've "grown", mostly in front of Rito. Haruna would get mad at her for when she talks about erotic things, especialy when she involves  Rito in it.

Yui Kotegawa
Risa is one of the people that Yui despises the most because of her indecent behavior like groping her's or other girls breasts, claiming her and also Mio shameless. However Risa also calls Yui shameless for having an attractive body. Risa would sometimes tease her about these sorts of things which further angers her, like asking if she has someone special.