I Am Worried That My Childhood Friend Is Too Cute! is a Manga/Manhwa/Manhua in english language, SUGGESTIVE series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

Amano, who returned to the city where he lived as a child for the first time in 10 years, meet Yukio Sawatari, a childhood friend on the first day of transfer, when he (a male friend) turned female! Although she shares her joy, as she suddenly turns into a girl and cannot hide her embarrassment. Yukio was affected by an illness like 100,000 other people, suddenly becoming a girl so-called " spontaneous isomerism metamorphosis ''!