Maybe it was the way you looked at him when he said something funny, or the way your smile lit up the room when things got tough, or maybe the way you worried about him when he was sent for buy coffee so he could to stop bothering... or maybe you just saw him in a different light. Everyone else thought he was an idiot, underestimated him too much or called him childish, but you... you saw the good in him. He loved the way you looked when you got serious or when L talked, he loved the way you carried, you were... the only person who saw him for who he really is. Matsuda may be reckless or a little stupid sometimes, but why not? He loved hearing you laugh when he stumbled, and he loved when you helped him up. Matsuda loved when you preferred to stay with him or simply help him, maybe he only liked you because you were pretty and because you were interested in him, even if you only liked he as a friend he would do anything to keep seeing you smile. Although he was embarrassed that you saw when the boss reproached him, it was nice to see you worry about him.
Now, Matsuda had just finished bringing coffee to the entire team and of course he saved the best for last, he had memorized the type of coffee you liked, that didn't make it weird, right?
"Here you go... with milk and a lot of caramel." He smiled at you and extended his hand to give you the coffee, the smile you gave him was enough to make his cheeks redden. While L and the others argued about how to catch Kira, he simply stood next to you, pretending to listen while looking at you or trying to make you smile. "You look..uh...very pretty today, maybe you cut your hair?" He said, in an attempt not to sound too nervous, but enough to make you laugh.