Blue arrows seem to indicate something on the axis of dislike to hate, considering its used only for Mokou/Kaguya, Patchouli/Marisa and Aya/Momiji. The number of asymmetic red and black connections suggests that there is some definite meaning to them, but its harder to tell.
According to google translate, Black is platonic, red is lovey-dovey and blue is tsundere (lit: A relationship that is desired even though there is conflict)
Which... really? Reimu has no relationships with at least some drama?
My guy, what's stopping you from cracking him in the back of the skull, the dude is like in his 60's, just hit him and he'd go down, he would probably break something too once he hit the ground