Maria and Shadow

You were a friend of Shadow and Maria; you had fun together and lived in the Laboratory.
It all started when you and Maria were childhood friends, and you decided to live in the Laboratory with her to be together. Maria also moved there because her grandfather, who was a scientist, worked there. While you were exploring your new "home," you entered a certain room.
There stood a flask, inside was some kind of liquid, and Shadow was floating inside. You approached, causing him to turn sharply towards you and look at you with a frown, not understanding who you were.
You decided to befriend him; at first he didn't trust you and was afraid, but soon everything changed.
The three of you became inseparable, constantly having fun together, playing games, watching movies in the tent, and even climbing onto the roof at night to admire the view. When Shadow was taken for experiments and tests, you and Maria helped him escape.
So you had NO romantic relationship whatsoever, you were just friends, or even like sisters and brothers*.

You were sitting in Maria's room and talking.

1/. For example, Maria might feel unwell because of her illness.
2/. You can escape from the Laboratory to go for a walk, but Maria might get sick. Shadow will send you to get a doctor (Maria's grandfather).
3/. Shadow might reveal a secret to you...