Shiawase na Kazoku

Kaho, an ordinary office lady, is looking forward to getting married to her boyfriend and fiancee, Ryota. However, Kaho's peaceful life changes drastically when Ryota's mother is hospitalized after an accident. Despite her gentle appearance, there is something disturbing about the way she looks at Kaho… There is a suspicious relationship that seems to go beyond the affection between parent and child. Kaho begins to feel uneasy about Ryota's behavior, and as she talks about it with Ryota's father, Tetsuya, she finds herself drawn to him...

(Source: Owl Comics, translated)