A dispassionate, withdrawn assassin, Golden Darkness is hired by one of Lala's arranged suitors, Lacospo to kill Rito, until she breaks the contract, noting the true nature behind her target. Golden Darkness came on a ship called Lunatique which is very quick (reaching a planet 30 million light-years away in 2 hours). Golden Darkness is currently staying on Earth, roaming around the city streets and Sainan High, with a motivation to continue her duty to assassinate Rito, although she has yet to accomplish this (hinting she only said this as an excuse to stay on Earth, which is then confirmed). Commonly referred as "Yami-chan", she spends her time reading books and magazines, while eating taiyaki (it is the only thing she eats on Earth since it is the first food offered by Rito, prior to spending a night at the Yuuki residence for a sukiyaki dinner). By her planet's (Kurosu) calculations, she is 24 years-old, despite having the appearance of an 11 year-old (albeit a rather mature one), although this is only mentioned in the anime and has a weakness towards anything slimy.
Like Lala, Golden Darkness' physical abilities are exponentially stronger than a human's. She carries a unique ability to turn her body parts into various objects through use of nano machines circulating her body, ranging from swords to dragon heads. Unfortunately, excessive use becomes a hazard to her health. She states she hates "ecchi" people, and does not hesitate to assault a person who looks at her in an obscene way. She has become close to Mikan Yuuki and seems to have developed a sense of protection for her, evident when she and Mikan switched bodies and the Principal attempted to grope her, to which she menacingly told him not to touch Mikan and delivered a savage beating. Though she always says she will kill Rito one day, it is doubtful she will ever do it. In fact, as of chapter 159, she seems to have begun to develop feelings for Rito. Instead of beating him and saying "I hate ecchi people" like she normally does, she blushes when Rito saw her in a swimsuit and stated "Don't look at me with those ecchi eyes". She even went as far as to go against something slimy to save Rito.
In To Love-Ru darkness, after some convincing from Mikan becomes a fellow classmate with the rest of the class as well as takes cooking lessons from her. Despite her normal emotionless appearance, it is easily noticed that she does care for Rito, where she put effort into making Rito's meal special. However, her new life may already be in jeopardy when Mea, a fellow classmate, is revealed to be her 'little sister', suggesting she return to space and to kill Rito.
Recently, it is revealed that Golden Darkness's creator is also named Professor Tearju by the assassin Kuro.
She is based on the young girl from Black Cat, Eve, seeing how they both can turn any part of their bodies into a weapon. Also they're both voiced by Misato Fukuen in the anime.
Also, in chapter 61 of the To Love-Ru manga and Motto To Love-Ru 10 (Episode 4 Act 1), "Yami Yami Fashion", Golden Darkness tries on a black dress similar to the one that Eve wears in the final chapters of Black Cat.