Jellyfish Restaurant

クラゲの食堂

Also known as Kurage no Shokudō, Kurage no Shokudou, 水母的食堂, Jellyfish Diner

Yōtarō Misaki finds himself lying on the beach one day. He is picked up by Arashi, who manages a restaurant called Kurage no Shokudō. When asked who he is, the protagonist tells a lie that he lost his memory — but he remembers everything, including the fact that his twin brother died.