Many individuals don't understand why someone would ship Graylu or think it's just due to Gray and Lucy both being "hot", which for some it is but not for me. So here it is laid out, I know many people will bash me for this but I just wanted to lay it out so maybe Graylu fans will not get as much hate.
First: I see Graylu as one of the few couples that could work in the real world. They both are rather normal and I think there friendship could become more. Also there personalities seem like they would work well together. They both find the same things funny and are very comforable with each other.
Second: I like how they are both saucy. They like to make fun together and joke around atleast in the anime. I find this cute especially when they were joking about Ichiza and the trio.
Third: While it was just a scene in the anime it's what made me orginally start even thinking about Graylu. The episode where it's Erza's "funeral" and Natsu is anger, Lucy is heartbroken and wants Natsu to stop. The person who was there for Lucy was Gray. It showed me that if something ever happened to someone special to Lucy, Natsu wouldn't be the one comforting her, it be Gray. I understand everyone would look at grief differently but in this situation it shows that Gray and Lucy would be there for each other.
Four: It's my general idea of what love is. Two friends who are always there for each other through everything, and sooner or later they realize there more. Your idea of love maybe Nalu or Gale or Jerza or Gruvia or something completely different mine's Graylu.
I have other reasons but I'm going to stop here for now and do part two later, since I need to get back to work. I may go more into two and three if you want me to also I could on one more.