" (親戚の子とお泊りだから), this subject refers to a Japanese media property, likely a manga, light novel, or adult-oriented animation (OVA) given the descriptive title which translates roughly to Media Overview
If the keyword resonates with your interests (autumn sleepover stories with a relative’s child, high-quality art), follow these steps: shinseki no ko to otomari dakara aki extra quality
You can find fan-made and high-fidelity renders on sites like ArtStation by searching for the character "Aki." Retailers: likely a manga