Say "I Love You." - Season 1 Episode 4

Mei has attracted the attention of one Kakeru Hayakawa, a guy known to have slept with many other girls, including Aiko. He then wastes no time in asking Yamato if he can hook him up with Mei for lunch with him. Yamato is unaware, though, that Kakeru has other designs for Mei, and, when Yamato was distracted by a phone call, he tried to convince her to be his girlfriend. But Mei sensed his motives and leaves him alone in an instant. Yamato learns of what happened, and when Kakeru starts badmouthing Mei, he punched him, saying she's his girlfriend. Kakeru tells Aiko about this the other day, but, despite being surprised about this development, she instead scolds him, that he will not be like Yamato. Mei appears to them, adding her impression of Kakeru. As he leaves in disgust, Mei, while recognizing Aiko's sacrifices, states that she is not giving Yamato up.