I was concerned if Rintaro dyed his hair black secretly without letting anyone know, least of all his girlfriend, but I'm glad he did tell Kaoruko, and he told her first. This was something he was doing mainly for her sake, so she should at least know about it; (although it's probably also a sign that he's really getting better from the time he needed to do it for himself).
"Kaoruko-san"
He switched to calling her first name instead of her family name. This is actually a big deal for Japanese people.
"If changing how I look can protect what I care about, I won't hesitate for even a second."
If it works, it's a cheap price to pay. Rintaro wasn't even dyeing his hair to express his individuality or anything: as someone else pointed out, it was largely a coping mechanism, that he perhaps doesn't need anymore. And I love how they actually addressed how Kaoruko wasn't so superficial as to only like the blond-haired version of him. She was concerned because it meant something important to him, but Rintaro doing this means he has something more important in his life now. Someone.
Her.
"Let's tough this out
together."
Relationship goals. A beautiful relationship between equals walking the same path in life.
Man, why are these two so precious? This manga just keeps hitting all the right notes for what I want to see in a romance. I might sound like a broken record by now, but what can I say? I love this. A lot.