Maria = tail up (happy)
No Maria = tail down (sad)

This bait is poor.
Shadow's way of showing love towards Maria is very nontraditional and indirect. While he's not able to understand a lot of acts of affection, he lets her show affection to him - something he wouldn't let anybody else do. And it's clear from his body language that he loves her.
You don't die for someone you don't love. You don't allow painful tests to be performed on you for their health. You don't remember their name and voice even after your memories were wiped. Shadow does that. Because Shadow loves Maria. And Maria loves Shadow.

>
>シャドウ、あなたがアークにいてくれてよかったわ
>Shadow, I'm glad you're here on the ARK
>
>ここのスタッフは素敵な人ばかりだけど
>あなたが来るまでとても寂しかった
>The staff here are all wonderful, but
>I was so lonely before you came