Short answers, pulled from the story.
Necro is a playable character in Capcom's Street Fighter III: New Generation, introduced in 1997. His real name is Illia, a young Russian man from a lakeside village who was tricked by Gill's Illuminati into having his DNA altered, turning him into a living bioweapon codenamed Necro.
Necro was designed by Akira Yasuda, known by his alias Akiman. Yasuda built a paper clay model of the character for the sprite artist to reference during development. Despite designing him, Yasuda later stated in a retrospective that he felt Necro did not belong in a Street Fighter game.
Effie is Necro's girlfriend and a companion character created early in his development for Street Fighter III. She stands 152 cm tall and was designed in part by Akira Yasuda, who drew inspiration from his own girlfriend at the time. The team described her final design direction as "Roll-chan but from Blade Runner," a reference to the Roll character from Capcom's Mega Man series.
Necro was originally voiced by Michael X. Sommers in Street Fighter III: New Generation. Lawrence Bayne took over the role for Street Fighter III: 3rd Strike.
Street Fighter series director Takayuki Nakayama confirmed that Effie was considered for inclusion in Street Fighter V. She was ultimately rejected because the team considered her "a very difficult character" to include.
Reception was mostly positive. Paul Furfari of UGO.com called Necro a welcome if difficult-to-play addition. Critics at Paste described him as an interesting addition and hoped for future appearances. Some outlets, including GamePro, were more critical and felt he belonged in Capcom's Darkstalkers series rather than Street Fighter.