sister product; related product
Used in business and marketing to refer to a product that is closely related to another, often sharing a brand, technology, or target market. Similar to 'sister product' in English.
This new product was launched as a sister product to the existing hit item.
The development of related products strengthened the brand's lineup.
関連商品 is a broader term for 'related products' in general, while 姉妹品 implies a closer, more intentional pairing, like a sister product.
Compound of 姉妹 (shimai, 'sisters') and 品 (hin, 'product'), literally 'sister product'. The term uses the sibling metaphor to indicate a close relationship between products.