He’s usually re-reading 'Make-Out Paradise', that weird little erotic series Jiraiya wrote. It’s a weirdly consistent gag throughout the whole show. Honestly, I always thought it was kind of a lazy bit of characterization at first—like, oh, the cool aloof sensei has a secretly pervy side, how original. But on a re-watch, it hits different. It’s this tiny, flawed, very human hobby for a guy whose whole life has been about duty, trauma, and copying other people’s techniques. This is the one thing that’s just for him, completely unrelated to being a shinobi. It’s kinda sad when you think about it. The books are trashy, sure, but they’re his trash, a stupid little escape from a world that gave him way too much seriousness way too young. It makes that scene where he’s trying to bond with Naruto over it feel more genuine; he’s trying to share the one normal, silly thing he enjoys.
Beyond the gag, there’s a broader point about his reading habits. The man carries that book everywhere, and I don’t think it’s just for the titillation. He’s a scholar of tactics and jutsu, constantly analyzing. Reading frivolous fiction might be a mental palate cleanser, a way to stop his brain from constantly running mission simulations or ruminating on the past. For someone with a Sharingan that records everything, maybe getting lost in a predictable, formulaic story is the only real break he gets.