Japan is renowned for its innovative beauty and skincare products, and lip serums are no exception. Here are some popular lip serums in Japan that are highly sought after for their efficacy and clean beauty principles:

1. DHC Lip Cream: This lip serum is a cult favorite in Japan. It is enriched with aloe vera, olive oil, and beeswax, which are known for their hydrating and nourishing properties. It also contains Vitamin E, a potent antioxidant that helps protect the lips from environmental damage.

2. Shiseido Benefiance Full Correction Lip Treatment: This lip serum from Shiseido, a leading Japanese skincare brand, is known for its anti-aging properties. It contains hyaluronic acid, which helps to retain moisture, and retinol, a form of Vitamin A that promotes cell turnover and collagen production.

3. CANMAKE Lip Serum: CANMAKE is a popular Japanese cosmetic brand known for its affordable yet effective products. Their lip serum is infused with honey and royal jelly extract, both of which are known for their moisturizing and healing properties.

4. NIVEA Rich Care & Color Lip: This lip serum from NIVEA is popular for its dual function. It not only moisturizes the lips but also adds a subtle tint. It contains natural oils and shea butter, which are known for their hydrating properties.

5. Ettusais Lip Essence: Ettusais is a Japanese skincare brand that focuses on acne care. Their lip serum is formulated with royal jelly and glycerin, which help to keep the lips moisturized and plump.

Remember, the effectiveness of a lip serum depends on the individual's skin type and condition. Always patch test a new product before using it regularly.