A dispassionate, withdrawn assassin, Golden Darkness is hired by one of Lala's arranged suitors, Lacospo to kill Rito, until she breaks the contract, noting the true nature behind her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 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 was the only thing she ate on Earth since it was the first food offered by Rito, prior to spending a night at the Yuuki residence for a sukiyaki dinner). By her planet's calculations, she is 24 thousand years-old (as shown in season 1 where the job applicant stops Konjiki no Yami just before she was about to say 'thousand'), 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, even if it's her own fault like when she was using her abilities to increase her bust she attacks Rito when he saw her, mostly out of embarrassment or for many occasions standing at the top of something such as stairs where her panties could be seen by accident. She has also stated, that she doesn't understand if she can feel love and all its wonders, though she slowly becomes closer to Rito once seeing that he is a good person.

Seto Kaiba is the majority shareholder and President of his own multi-national company, KaibaCorp, who aims to become the world's greatest player of the Duel Monsters card game. To accomplish this goal, he must defeat his arch-rival, Yugi Muto. He is largely considered an anti-hero, as his motives are usually ego-centric, but in several cases towards a good cause. Kaiba was first introduced as a prodigious, cold-hearted gamer who stopped at nothing to achieve his goals, even resorting to seemingly killing his opponents. He lived a bad childhood because of his good for nothing stepfather. When Kaiba learned that Yugi's grandfather possesses a "Blue-Eyes White Dragon" card, he ends up dueling Yami Yugi and lost while ending up in a coma after Yami used his power to momentarily shatter Kaiba's heart to purge it of his evil. Though reformed, later learning his rival's identity to be Atem, Kaiba retains his arrogance and rivalry with Yugi. While Kaiba leaves the story following the Battle City arc, he appears in the anime adaption as a major character and has been mentioned in sequel Yu-Gi-Oh! GX series as the founder of Duel Academy. Among one of the recurring plots in Yu-Gi-Oh! Duel Monsters is Seto Kaiba being forced to deal with either people adversely affected by Gozaburo Kaiba's actions wanting to take their revenge on Seto Kaiba, or people from within KaibaCorp attempting to take over the corporation. He can be condescending, selfish, no-nonsense, and narcissistic, but, as Yami Yugi has said he can be oblivious at times. However, it is stated by Mokuba ever since being adopted by Gozaburo, Kaiba became much colder than he used to be. Despite this, Kaiba still has strong brotherly instincts for Mokuba and will put his life in danger in a heart beat to safeguard Mokuba's life. Apart from Mokuba, Kaiba has compassion for children—especially orphans (as he himself was one and knew what it felt like). Kaiba also threw himself between Zorc and two Egyptian children, thus enabling them to make a getaway. At various points during the series, he opens up momentarily, performing kind acts, though always covering them up with sarcasm, and denying them if asked. These occurrences increase in frequency towards the later series. Aside from that, Kaiba maintains a conservative, stiff, and uptight exterior. Like the Pharaoh, pride is Kaiba's strength and weakness; he never backs down from a fight and gives everything he can in a Duel. This results in his sense of superiority and sense of arrogance, making it extremely difficult to earn his respect, and causes him to look down on and treat others as inferior until they do so. This gives him difficulty when forced to rely on others and work as a team. His pride in himself and his accomplishments is a prominent part of his character throughout the series, and he reacts harshly to those who threaten or infringe on it (although it is toned down slightly towards the end). (Source: Wikipedia, Yugipedia)