>>534926763
Maria is Shadow's Amy, essentially. What Maria herself actually becomes is a blend between a simple childhood friend that's basically a sister figure crossed with a love interest in some way, but also an older, motherly kind of nurturing caretaking role as she's the one who basically helps Shadow learn about the world and stuff. It's why some people can compare it to a girl and her dog, even though that itself is not "true" to what Shadow and Maria actually are to each other.

Either way, Maria was "everything" to Shadow. Imagine someone whose like your best friend, your sister, your girlfriend, your mother, your teacher, etc, all in one package. And she gets shot down dead right in front of you. YOU, the ULITMATE LIFEFORM who exists for the sole purpose of making sure that girl DOESN'T die. That's the kind of pain Shadow feels. The kind of empty hole that destroys him on the inside, and makes him want to destroy everything else in her name. But that's not what Maria would have wanted. His purpose is for her, so he shall fulfill her wish. Anything else is pointless, irrelevant and doesn't matter. Throw it all away.

Rouge is the polar-opposite of Knuckles, in the form of his weakness (Women), and her calculative charming personality is a direct contrast to Knuckles' straightforward yet very trusting mindset. But Rouge's debut is on the Dark Side with Shadow, so Shadow and Rouge are allies. So, with Shadow, we see Rouge eventually become very affectionate and caring towards him, especially since he's so cold, so the Sonic/Amy side of Rouge is triggered in a "come on, open up and enjoy life" kind of way. This then means that Rouge becomes a Maria-figure for Shadow, in a way that contrasts with Rouge's outer appearance as a manipulative backstabbing spy who only cares about what benefits herself.

Shadow has some sort of subconscious need for an older, maternal-esque role in his life to pull him out of his shell, and that's exactly what Rouge is for him.