Agatha Hex

Agatha Hex is a major character in the overall story of Five.

Design
Agatha appears as a young woman (18-22 years old) and has an overall creepy appearance, although she can clean herself up for a more normal one when the situation calls for it.
 * Long dark unkempt hair
 * Pale skin
 * Typically wears a creepy smile. This can actually intensify into the insane villainous faces we see in the Yu-Gi-Oh! anime series when she gets fired up in a duel.
 * Wears a dark cloak that covers her whole body. She gives off the impression that she belongs to an occult cult.

Personality
Just like her appearance, she has a creepy demeanor that unnerves the people she interacts with, even Silence and the Thief. Despite that, she is also always polite to the same people. Because of her creepiness, though, the people aren't sure if her politeness is for real or if she's just messing with them.

After officially allying with the Winner Five, her personality doesn't really change. But, now that the characters know that she has been trying to help them all along, they know that she really is a good person and are able to get along with her much easier.

Planned Role

 * She would actually be directly involved in the overall plot of Five, so she would appear over multiple seasons.
 * For Season 1, she will play a minor role.
 * She is someone hired by Silence to help Kazuo out during the Captivity Arc.
 * At the same time, the Thief is also familiar with her and they will interact giving the false hint they are allies.
 * However, both Silence and the Thief don't completely trust her, and she gives off the impression that she is actually working independently and has her own agenda for Nexus and the technology behind it.
 * Her role in Season 2 hasn't been thought out yet, but it will be revealed that she was actually involved in Eisuke's tournament of Season 1 from behind the scenes.
 * Overall, with each passing Season, she will steadily take a more active role until she becomes one of the main characters.
 * She would serve as an antagonist/rival to each member of the Winner Five. She also has disturbingly accurate knowledge of each member's background, which allows her to set up obstacles that will require the Winner Five to confront their problems and grow in order to overcome them.
 * Eventually, probably in the final season, it's revealed that she's actually an ally of the Winner Five. Her antagonism in the previous season towards the Winner Five were to push them to grow stronger so they can be ready for the final season's threat.  She would then officially join forces with the Winner Five and their allies and continue to play an important role defeat the final season's threat.
 * Some ideas about her identity
 * She is actually a manifestation of whatever powers Nexus (Cogito?), just like the Observer. However, she is completely separate from the Observer and has a will of her own.  She can be like a sibling of the Observer.  She grows as a "human" much more quickly than the Observer since she also interacts with people rather than just observe them.  The result is that she can pass off as a quirky human from the beginning, but it comes at the cost of not being able to control technology as well as the Observer possibly can.  Since she will play a pivotal role in the overall story of Five, this may be a suitable identity for the character.
 * Or, she can be a private investigator. Her client is someone who was close friends with the Professor and was secretly involved in the project too.  However, the Professor's death, the client hired the character to find answers regarding Nexus and Cogito, which leads to the character getting involved with the Winner Five.

Deck

 * She will play various Ritual decks throughout Five.
 * At first, she is actually new to the game of Yu-Gi-Oh! unlike the Winner Five and other prominent duelists. So, while she'll be able to put up a fight, in the end, her opponents will defeat her without too much trouble.  But, as the story progresses, she quickly adapts to the game and becomes a much bigger threat like Bohman from VRAINS.
 * After every loss, she will change to use a different Ritual archetype.
 * Eventually, by the final season, she will finally find the Ritual archetype that works best for her and will stick with that for the rest of the story.