Koijama na Osananajimi ga Mukatsuku

Overview

Yuujin, a high school student, lives with his childhood friend, Chihaya, and Chihaya's younger sister. While Yuujin secretly admires Chihaya for managing to care for his sister while searching for his missing father, he also sees him as a rival. When Yuujin's parents grow frustrated with his lack of focus, they ask Chihaya to be his "chaperone." Acting like a bodyguard only makes Yuujin more irritated. One day, after an older woman confesses to Yuujin, he brags to Chihaya about having his first girlfriend. Chihaya replies, “Let’s practice wearing a condom for when the time comes!” When Yuujin refuses, Chihaya decides to demonstrate... right in front of him! (Source: Houbunsha, translated) Note: Includes two extra chapters.

Source: AniList