Shin Sei Yariman Gakuen Enkou Nikki Part 1 新・聖ヤリマン学園援交日記
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Based on a doujin game by Orcsoft.
Saiki Yasuo is a 45 years old office worker. After 20 years of marriage, his wife asked for a divorce and left him. Now, depressed, he spends the nights drinking alone, until one night a girl from the St. Marian Academy approaches him looking for a client.
(Source: English DLSite)