Runaway Girl

A college student coming home from his part-time job runs into a girl in the rain who apparently ran away from home. Pity takes the better of him when invites her out of the rain and into his home to warm up for the night... only for him to realize that she wants to repay the favor with sex...

(Source: Fakku!)

Note: Originally self-published under the title Iede Gal ni Nama Nakadashi Shimakutte, Seishori Dousei Hajimemashita (家出ギャルに生中出ししまくって、性処理同棲始めました).