An odd one, but I was wondering if there are any series where there is some undeniable proof of a person having feelings for another. May be just proof that they're in love with someone, may go so far as to prove exactly who they love, but something that's completely and directly connected to this feeling and thus can't be denied or dodged with excuses. My whole example will have to go in spoilers since the fact that this is about love is not known until near the end in this particular series

In Shishunki no Iron Maiden, the heroine has a "condition" where her body occasionally releases massive amounts of iron through the skin, producing a sort of exoskeleton-like structure. Near the end it's revealed that this condition only manifests in girls who have a crush or are in love with someone, and a lot of characteristics of the exoskeleton depend on aspects of that love. For instance, as the girl gradually develops feelings for her childhood friend a pink color starts to develop and spread, drowning out the dark red from her love for her senpai, and even spreads past where the exoskeleton originally covered.

I think Dear Signal is perfect then

Scorching Romance sort of fits too