湯けむりの背徳交姦 ～幼なじみは、兄嫁で、若女将で、未亡人でした～

The protagonist, Hayama Junpei, is similar to his brother in both looks and personality, but not in skill and talent, as his brother was superior than him. He returned back home for the first time in 5 years after hearing news of his elder brother's sudden death. He then decided to stay home and help with the ryokan until his summer break ends. 

One night, Junpei found Yuka asleep in the floor after she seemingly drank her sorrows away. Not wanting for her to catch a cold, Junpei woke her up and asked her to sleep properly in a bed. Still drunk, she thought Junpei was her husband, and asked him to have sex with her. Junpei tried to refuse at first, but eventually he accepted her seduction. 

Halfway through, Yuka sobered up, and was surprised to see Junpei having sex with her...