Level 999 Oldbie, Eaten by a Newbie

'''Introduction to the Work: "I'll take it, your first experience." An otherworld where everyone possesses skills. Shu, a skill holder at level 999, saves Sosi, who has just arrived here for the first time, from monsters. As he brings him home and teaches him about this world, the atmosphere becomes suggestive, and... At that moment, due to the 'Steal' skill Sosi discovered, Shu becomes level 1. The only way to fix this is through seX?! "Let's raise our levels together in bed." Don't tease me, old man...! Shu's otherworld life, where his level and first experience are both stolen by a bold newbie!'''