S.I.S.T.E.R is a group of six feminine heroines. They are each the counter-balance form of the Super Squad. Each of the girls is a sister to one of the members of the Super Squad. This team consists of Susie, Isabelle (Isa), Sally, Tess, Emma, and Rachel.
Susie is the main leader of S.I.S.T.E.R. She is very powerful and skilled in her battle tactics. She has the powers of Space. With this power she can summon any objects from space (meteors, asteroids, comets, etc). She is very mean like the rest of her teammates and she absolutely hates Ace for an unknown reason. She is the only member of her team not to appear before chapter 10.
Isa is a member of S.I.S.T.E.R. and is the identical twin sister to Roxy (3 minutes and 27 seconds older). She mostly uses her powers of mud to attack others, but she has been seen using the power of earth in Chapter 4. Because is twin sisters with Roxy, she is assumed to have the same powers as her. She is one of the younger members of S.I.S.T.E.R. being only 11 or 12.
Sally is the youngest member of S.I.S.T.E.R. She is very cheerful and acts as if she was six years old. Her powers derive from rainbows and any magical creature (faries, unicorns). Her part of her hair is made from rainbows which enable her to extend her hair to any length or size. Sally is the younger sister of Will Guy . Although she is young, she is very powerful.
Tess is a teammate in S.I.S.T.E.R. She has the powers of Water. She, along with Emma, is a sister of Aquais . She is also a young heroine. She is princess of the Oceans and Sea Dimension. The only reason she has her powers is because her father gave them to her because she is part of his family. It is debated that Tess left her real family (the Bay's) because the book says Aquais is an only child.
Emma is the older sister to Aquais and Tess. She also is a princess of the Oceans and Sea Dimension. She has the powers of Ice and it is unknown whether she can control water like her brother. She is very mean to Aquais because she should be the rightful heir to the throne ("The Underwater City" 11-11). She is the second oldest member of S.I.S.T.E.R.
Rachel is the oldest member of S.I.S.T.E.R. She is the only member of her team that is not related to the Super Squad by blood. She was taught by Inferno so technically she could be considered a "sister" of him. She controls magma and is very powerful. She can even force an entire volcano to erupt on command. Inferno states that she used her powers to wipe out an entire city in the past. ("S.I.S.T.E.R". 10-11)
Each of members of S.I.S.T.E.R. has a cameo appearance in either Chapters 3 or 4 with the exception of Susie. They are all allied with Copy Cat. The girls ambush the Super Squad on their (Super Squad's) road to Sacramento The girls exhibit great skills in control of their powers an most of them win against their brothers. They launch a final attack to destroy the team once and for all. However, S.I.S.T.E.R. is quickly defeated once the Super Squad uses their Super Form. At the end of the battle, Susie promises their return to defeat the Super Squad
- The name "S.I.S.T.E.R." most likely derives from:
1. The fact that they are "sisters" to the Super Squad
2. Their names spell out S.I.S.T.E.R. (Susie, Isa, Sally, Tess, Emma, Rachel)
- They are listed in the same order as the Super Squad [Ace (Susie), Roxy (Isa), Will Guy (Sally), Aquais (Tess and Emma), Inferno (Rachel) ]
- Tess and Emma are the only girls that share the same brother (Aquais)