My Tsundere Childhood Friend... I Got A Girlfriend, And She Says She's Training Me To Improve My Premature Ejaculation And Has Jealous Self-promotional Sex With Me... Airi Nagisa

Nagisa and Higashi have been childhood friends with a love-hate relationship, always arguing whenever they open their mouths. Higashi, now a high school student, starts his first relationship with a female classmate and is on cloud nine. Behind the scenes, Nagisa secretly receives a consultation from the girlfriend that 'Higashi is having trouble with premature ejaculation.' Despite mixed feelings, Nagisa offers to be a practice dummy for blowjobs under the guise of 'training'... Is it an extension of teasing, jealousy, or something else...?