lulu la morue

they were both imprisoned on the same ship

keith is only able to find red because shiro’s advice led him to her 

red is the right arm of voltron, and thats the arm shiro lost 

when shiro interrogates sendak, he literally thinks to ask how they got the red lion before even asking about zarkon’s greatest weakness (the fact that he asks how to defeat zarkon right after makes me wonder if one has anything to do with the other)

this 

shiro and red are really injured at the start of season 2, and keith reassures them both–“Okay. We’ll fix you up” “Hang in there. When allura and coran find us, they’ll fix you right up”

like allura, shiro’s flown in the red lion before

when keith is getting seriously hurt in his bom trial, shiro and red literally start lashing out at the same time (when they notice red’s at the base attacking, the bom have already had to restrain shiro). and both he and that lion are literally willing to fight everyone at the base if it means protecting keith 

the red lion being noticeably present in the background when shiro is shown in the last episode (in the case of when he blacks out, we know that lauren montgomery storyboarded that, so it was intentional)