Kujō Rin

Rin Kujou is Saki Tenjouin's loyal and longest known friend. Rin is skilled in kendo and has been a loyal bodyguard to Saki for years, as her family has always served the Tenjouin family in this position. The bespectacled Aya Fujisaki is weak-willed and became associated with Saki after she and Rin protected her from bullies when they were children.

While Rin is very loyal and caring to Saki, she is also very dutiful. These made her conflicted when Saki once ran away from home, and Rin was ordered to bring her back, even by force. But after Saki managed to settle things with her family, she and Rin were able to remain friends.

Rin is usually calm and very composed, and is perhaps the most mature character in the series, at least among the students, despite how few moments her character was explored without being together with her friends. Like Saki and most other girls, she is also not completely safe from the antics that surround Rito Yuuki, and naturally, she has a negative impression of him, but she has shown few instances of potential to understand him better and perhaps grow more patient with him.

Throughout most of the series, Rin is hardly ever seen without accompanying Saki Tenjouin and/or Aya Fujisaki, and has interacted personally with very few other characters in the series. However, in To LOVE-Ru Darkness, she has caught the notice of Momo, who is considering adding her to the Harem Plan, hoping that Rin would open up to consider Rito as a love interest.

Appearance
Rin has brown eyes  and   hair, to which she has a pony tail with a blue scrunchie. Rin is often seen with a motionless face.

Personality
Rin is seemingly expressionless and formal but can get really angry when it comes to Rito's clumsiness towards her, Aya and most of all Saki who  she shows her most loyalty to and her family. Although she has show to smile practically once to Rito as a sign of understanding, it didn't last long due to another one of his mishaps. She thinks his sister is more reliable than he is. However, Rin may have develop feelings towards Rito in Darkness Chapter 33 when he saved her and seems to blush around him.

History
Rin has served Saki as her bodyguard, but Saki has always thought of her as a close friend instead. They first met when Rin came to Saki in the garden introducing herself as the daughter of the Tenjouin family's butler and then tells her that she will be serving her starting from that day. Saki acted friendly towards Rin and welcomed her company as her friend, and Rin was deeply touched by it. Although most of the time, Rin maintained a professional manner and service around Saki, she truly considers Saki as a close friend.

Powers and Abilities
Rin is known to practice Kendo, and is often seen carrying a shinai. The only times she is seen using Kendo are either when training or when she's mad at Rito whenever his clumsiness results in him groping her, Saki or Aya. She has also beaten up the principal time from time.

Because she does not involve herself with Rito, his alien friends, or their adventures and antics, she is mostly left out of any potentially dangerous situation, and so the full extent of her expertise in Kendo have not yet been seen.

On chapter 83 she has shown to also have some sniping skills.

Saki Tenjouin
Rin is Saki's bodyguard and the oldest and closest friend she has. Her family has served the Tenjouin family for generations. Rin shows great loyalty to Saki and gladly accepts any request she gives her regardless of what it is. Rin has deep desire to protect Saki from any danger.

Saki considers both her and Aya to be her closest friends, to the point that Saki ran away from home rather than be forced by her father to study abroad without her friends. Rin, on the other hand, while caring for and greatly respecting her, is a little more divided between her loyalty to her Saki-sama and obedience to her family, who serve Saki's family. This was seen when Saki ran away from home, and Rin arrived to bring her back by force rather than support her. Ultimately, Saki did not leave to study abroad, and they were able to remain together.

In To Love-Ru Darkness, after Rito Yuuki saved Rin from being possessed by the sword, Bladix, Saki noticed Rin's bashful expression towards Rito and claims it might be love. Because she has never seen Rin act this way before, Saki happily decides that she will support Rin's feelings, even if it's towards Rito.

Ayako "Aya" Fujisaki
Even though Rin and Aya are always seen together with Saki and they both admire her, they don't exactly have any other thing in common and Aya shows more admiration to Saki than Rin does, as Rin often shows less emotion.

They first met each other when Saki and Rin saw Aya being bullied by a group of boys, and Saki insisted on helping her, while Rin just followed her. Since then, Aya has always followed them.

It's not quite known how Rin and Aya feel towards each other. They are friends to each other, but more often follow and pay attention to Saki, and have not often been seen interacting directly to each other.

Mikan Yuuki
In To Love-Ru Darkness, Rin has established a better relationship with Mikan then with her older brother Rito. It began when Mikan fainted on the streets on a hot day and was found and taken in to Rin's place, who showed her hospitality. Rin also believes that she is more reliable than her brother and would ask for her help instead, although Mikan tells her that Rito can be counted on when someone is in trouble, which was proven true some time later.

Rito Yuuki
Rin dislikes Rito's perverted clumsiness, especially around her, Aya and most of all Saki, and doesn't hesitate to hit him for it with her wooden sword (sometimes with a real sword, and on one occasion, she used a gun on him). One time, she and Aya requested, or rather forced, Rito to arrange a meeting between Saki and Zastin, and when he helped them, Rin has shown a slightly better understanding towards him (even willingly smiled at him), but unfortunately, that did not last long before Rito's clumsiness struck again, ending her short-lived respect for him.

She has shown kindness and hospitality to Mikan, and finds the younger sister to be a lot more reliable than her brother. In To Love-Ru Darkness Chapter 31, she asks Mikan to help work in the Tenjouin mansion, but Mikan instead requests that she accepted Rito in her place, persuading her that he can be counted on when someone is in trouble. Unfortunately, Rito's clumsiness persists to harass her and Saki, despite his best intentions. Rin feels that she's just unable to think of him the way Mikan does.

However, some time later, after Rito saved her from being possessed by the sword, Bladix, she appears to have changed her impression of him. She is now grateful to him, but this time in a clearly more bashful way, which is highly uncharacteristic to her usual composed and aloof self, and she likely has begun to grow affectionate feelings towards him (To Love-Ru Darkness Chapter 33).

Trivia
Rin made a cameo appearance along with Saki and Aya in Mayoi Neko Overrun! in Chapter 3 page 24.