Kokoro Tsurumaki

A happy-go-lucky student at Hanasakigawa Girls' High School and the leader and vocalist of Hello, Happy World!. Her family is ridiculously rich and lives in one of the biggest houses in the area. She's the only member of her school's astronomy club.

Kokoro is an idealistic and charismatic young girl whose goal in life is to make the entire world smile. She effortlessly attracts others to her with her bright and bubbly nature, often sweeping them up into her easygoing pace. She is easily able to do and get what she wants, no matter how absurd the request, mostly thanks to "the suits": three bodyguards that follow Kokoro around that can seemingly accomplish anything she wants like magic, appearing out of nowhere when they're needed. As a sheltered rich girl, Kokoro is ignorant about certain normalities like taking the train.

Kokoro is also very curious and easily amazed, charmed by new things she discovers in the world around her. Even though she has the optimism and charm of a natural leader, she appears rather scatterbrained and unable to accomplish much without others' help. Despite this, however, she has also shown hints of being something of a genius with her ability to master almost any skill instantly, and of being surprisingly perceptive to the people around her, although she rarely shows it. Kokoro doesn't seem to understand negative emotions; she's stated that she doesn't know what it feels like to be sad, and Marina once had to explain to her what it means to be stressed. Kokoro describes people who aren't happy as simply not smiling or having "forgotten their smile", and as per her dream, she does always her best to combat any kind of negative feelings.

(Source: BanG Dream! Wikia, edited)