The marriage contract of Ryuo no Ko is sweet and indulgent / 未白 Mine

Product description ※Please note that product information is not in full comprehensive meaning because of the machine translation.

Celia, the countess of the Long-Lived Race, is offered a marriage proposal to Alsto, the second prince of the Kingdom of Asselah. In fact, Alsto, who was in a condition with no end of life, had the purpose of sharing the life of Celia and extending the life of Alsto by "getting engaged" with Celia, who has a long life. Celia made a temporary contract to extend the life of Alsto for a limited time. However, in order to share the life, Celia needs to have an affair?