This squad is not complete. For exemple, Ibaraki is here so where's Shuten? Also, Medusa lily, Euryale and Stheno? Helena? Mary Read? Illya? Chacha? Abigail may be too recent to be in I guess.
None of those bar Abigail and Illya have childish characters. Shuten is very much an adult in mentality, Helena is basically herself from the end of her life slapped into her body from her youth, Euryale and Stheno act like the capricious Greek goddesses they are, Chacha is the same deal as Helena with the addition that her younger personality is dominant, Mary Read is a pettanko and has a mature personality. Medusa Lily is still Medusa at heart, so she's very much a "sane man" type of character.
Illya definitely does count though, but her "unit" is the Emiya Family.
If I had to guess why these characters in particular were drawn together: The first four all have strong in-character ties shown in the story. They're a well known group of friends. Ibaraki's personality would fit her in to a T, as the biggest thing I've noticed regarding her characterization is that A) she is childish (something Shuten teases her over) B) She has a sweet tooth (again, Shuten teases her for this). Wu Zeitan I've seen very little of, however I wager that she's here because she's cute and an Assassin counterpart to Jack. What I do know of her however says she fits into the mould of Helena and Chacha (both of which, it should be noted, have their own "units": Tesla + Edison and the Koha Ace crowd respectively).
This squad is not complete. For exemple, Ibaraki is here so where's Shuten? Also, Medusa lily, Euryale and Stheno? Helena? Mary Read? Illya? Chacha? Abigail may be too recent to be in I guess.
Shuten, Medusa lily, Euryale, Sheno, Helena, Mary Read is loli in body, not mind. Illya is in Emiya Family Squad. Chacha is the closest one, she might be not famous enough. (or wadakazu didn't have her.
