Stella's past before becoming an orphan are currently unknown. What is known so far is that her parents both died on a plane crash when she was 4 or 5 years old. It was also on that plane that she originally met Zeno. Both of them gained the scar on their right hands as the plane blew up and a gaint screw peirced their right hands while Zeno sheilded her. Afterwards both of them ended up in the same orphanage and later on were adopted by the Kuonji family. It is unknown if they had any prior relation before being on the plane as well.
Stella talks rather bluntly usually, even going as far as admiting to having a server 'brother' complex when turning down Tsukito in the first chapter. She can get rather flustered and childish when she's with her older 'brother' Zeno. She has a strong sense for justice or at least loyalty and finds this whole 'murder' game to be just plain insane.
Her Alter Ego 'Bloody Alice' has more of a blunt personality and can talk rather tauntingly and antagonizingly, wanting to get a reaction out of her opponent. She usually appears when Stella's life is in danger.