Japanese Child Pop Star Hirata Runa Dead at 8

A child pop star who was a trainee of the Japanese girls’ idol group DIANNA Project has died. She was only 8 years old.

Hirata Runa "passed away peacefully" on Sept. 25 ... according to her X account.

The DIANNA Project shared in a statement that the up-and-comer died "due to myocarditis resulting from influenza."

The group -- which asked for privacy on behalf of the family -- added ... "We extend our heartfelt thanks to all the fans who supported Runa Hirata and to everyone involved who provided their support."

Following her last performance -- which took place on Sept. 20, according to The Standard -- Runa wrote ... "Thank you for today too, I appreciate it. It was so much fun."

Just 8 days later, her team wrote on her X account ... "To all the fellow idols who were kind to Ruyu during her lifetime, to the fans who supported Ruyu, to everyone at the agency who made Ruyu an idol, and to all the people who were involved with Ruyu, thank you very much."

Myocarditis is inflammation of the middle muscular layer of the heart wall, called the myocardium ... according to the American Heart Association.

She was only 8 years old.