Chinatsu Yoshino (吉野千夏, Yoshino Chinatsu) is a supporting character in Sekai-Ichi Hatsukoi. She is the younger sister of Chiaki Yoshino.
Chinatsu has the same blue eyes like Chiaki and short dark brown hair. She has a fair skin tone. She is first seen in an OVA wearing just a regular pajama outfit at home. However, she later changes into something more formal due to the fact that Hatori was visiting.
Chiaki is Chinatsu's older brother. Just like regular siblings, they get into many fights. However, it is clear that they do love each other. Chinatsu isn't aware of Chiaki and Hatori's true relationship.
Chinatsu seems to have a crush on Hatori. This is seen when she walks downstairs when hearing Chiaki had arrived in a pair of pajama's only to become quickly embarrassed when seeing Hatori was there as well. She quickly scolded her brother for not telling her this before she changed into something more formal.