拝啓、天国の姉さん、勇者になった姪がエロすぎてーー 叔父さん、保護者とかそろそろ無理です ぷらす

A former strongest mercenary, he was injured and retired, then his fiancée ran away and he now spends his days drinking away his time as a middle-aged adventurer (a virgin). Then his niece Liz, whom he once taught swordsmanship, shows up to visit him! Angel is confused by how she has grown into a stunningly beautiful girl, but Liz has declared that she will marry him regardless of his feelings...!? A thrilling adventure fantasy in many ways, woven by a beautiful heroine and a middle-aged uncle!