|First Appearance||Chapter 108|
|Last Appearance||Chapter 122|
|Status||British Interpol Investigator|
Andrew Sixson (アンドリュー・シクソン) is a manga-only character and is a friend of Usui's that was dispatched by Interpol to investigate X. Andrew never actually makes a "real" appearance in the series, as Sicks merely disguised as him.
Andrew is a rather light-hearted British man with round glasses. He befriended Usui when Usui was an exchange student in England. Andrew has a distinctive laugh (Sh-ha Sh-ha)and is quite fluent in Japanese, though he'd rather speak English as he finds Japanese too advanced for himself. He has a countryside valve accent when he speaks English. Andrew appears to have a dandruff problem .The food he dislikes is Japanese ginger.
Andrew's has superb memory and is capable of memorizing vast amounts of information extremely quickly, picking out a single bit of information by listening to multiple radio stations at once, or reading through a stack of papers in an instant. It is later revealed that this was a result of being a relative of the New Bloodline, though Sicks states that this ability is nothing special.
Andrew is first seen meeting up with Usui to discuss about X, and reveals to Usui that Ai was X's partner. He is later seen gathering information on X and is introduced to Sasazuka. Soon,the both of them go to Yako's Detective Agency and find out about X's whereabouts. Neuro has defeated X by the time Andrew and Sasazuka reach X's hideout, and they chase him to the roof of the building, where X is about to leave on a helicopter piloted by Ai. Before X can escape however, Andrew shoots Ai and kills her.
At this point, it is revealed that "Andrew" is really Sicks in disguise. The real Andrew Sixson was captured by the New Bloodline before he even came to Japan and was tortured to reveal every single bit of information on himself. Sicks had Andrew killed off after that and had his face peeled off so he could capture X while masquerading as a member of the police.
- Andrew Sixson bears some resemblance to Light Yagami from the occult detective manga Death Note in terms of appearance and personality. Interestingly, Light Yagami also showed a sense of calm light-heartedness while he was speaking in person with his allies from the task force prior to betraying them and being exposed for his crimes by Near at the end of the series.