So when the Phantom guild attacks Fairytail that's when Gray and Juvia meet. They end up fighting with Juvia's water style and Gray's Ice make I automatically shipped them.
As a child The rain always followed Juvia so she was basically alone then Gray defeats her and is the only one that stopped Juvia's sorrow. After that Juvia's stalker ways and love for Gray was unconditional. Seeing any woman that looked, talked, touched, even thought about Gray was her romantic rival.
Juvia did anything for Gray, But due to Gray losing Ur and all of his family he didn't open up much. Eventually you can see how much Gray does care by protecting Juvia multiple times.
Then Lyon the love triangle is formed and you see Gray is jealous a few times. Juvia has even been living with Gray the whole time and when their powers combine they become the ultimate duo !!!! Juvia doesn't even judge Grays stripping habit she just holds his clothes. Now with the whole scarf episode just made them canon . If you have seen Naruto and Hinatas love story the scarf symbolizes love and it the same here.
I cried my eyes out when Gray shoved Juvia out the way. He died for her and if that ain't true love i don't know what is. It's from that point on you see Gray and Juvia get closer . Plus everyone in the Guild Ships them and even Lyon sees they belong together.
Now during the Tartarus arc is what I believe made their love ship officially canon she has to fight the demon who is controlling Grays father and the other council member that's about to turn on the faces that will take away everyone's powers. The pain Juvia must of felt to know that even though Gray reconnected with his father she has to take him away for good.
But in the end Grays father entrusted Juvia to take care of him. When Juvia realizes what she had to do she was willing to let Gray hate her in the end. Well Gray realized that what she did for him was unconditional love and he thanked her for it then stated "she was warm" .... In the end they both saved each other from years of pain. That's why I ship Gruvia!!!!
Plus I do relate to Juvia and how she felt beforehand meeting Gray just love them together . Oh yeah Grays super duper sexy !!!! Lol