Seiya Kou / Sailor Star Fughter

This is a relationship that even if it happens only in the final arc, it has to be mentioned, because Seiya is there for her, when Mamoru isn’t. And yes I do know that Seiya is a female. Seiya (along with Yaten and Taiki) is there when Galaxia takes Mamoru’s star seed and catches Usagi who fell unconscious.

For me this relationship is important because it seems as only Seiya can notice the burden that Usagi actually carries on her shoulders and still is caring, loving and dedicated to her friends.

“Have you always carried a burden on your wings?”
-Stars Arc, Act 46

And even if she should dedicated all her power protecting her own princess, she decides that after Usagi lost so many to offer her protection, not only her own, but also of her comrades.

“Sailor Moon, no matter what dangers await us we will stand by your side to protect you.”
-Stars Arc, Act 46

This is the relationship that comforts Usagi and gives her the strength to go on. Seiya knows how to make her feel better and understand that she is important.

“Your Hand.”
“I’m sorry for being such a burden.”
“It’s ok. You’re the princess. It’s ok to be protected. Princess. Become stronger by begin protected. Let’s go.”

- Stars Arc, Act 47

And this is also to let her know that it’s not only because of her crystal that she is strong, but because she was always protected by her friends – Seiya makes her understand that she is strong because of them, for them.