In her sealed form, she looks like a rose bud.
She looks a young girl with short hair. She wears a longsleeved dress. Her eyes may appear to be slits, much like a feline's, at times.
It's a bit hard to read her. There are times when she appears mischievous (such as during her and Maxi's first meeting), or serious. She doesn't seem to be naive, and calls Maxi one. She calls Maxi names when he fails to shoot his ARM and taught him. When he successfully fires it, though, she does a "V".
She appears to be close to Maxi after making him her avatar, encouraging him to find his answers when he's thorn between continuing his journey or going back home. He remarks on how she knows him so well, and she answers that they're one. She's doesn't hesitate to retaliate when Maxi is shot, but otherwise tends to leave Maxi to fend for himself.
She appears suddenly at times (and surprising Maxi in the process), or drags Maxi back into his mind (such as when she's teaching him how to shoot).
She is able to keep Upperhorse's lands fertile (despite being sealed) while the surrounding is desolate, drained of life. After becoming her avatar, Maxi once accidentally causes vines and plantation to grow.
She's capable to transporting both Jessica and Maxi into Maxi's mind, healing Jessica's arm back to the way it was from Maxi's arm data (and Maxi's by using her own body), and creating an ARM. The healing and ARM are carried over to the real world.
When Maxi is shot, the Guardian takes over, plantation growing around Maxi and creating a new ARM in an instant, planning to shoot the shooter. She's only thwarted when Maxi uses his other hand to force the ARM upward, blowing up the roof of the train carriage, shocking the shooter.
She seems to be familiar with how to fire an ARM, being the one who instructs Maxi on how to use his after he shoots badly.