i get all the points about zeff and not being interested in girls because hes mentally 60 but hes also not, its been shown that his current younger self has his own will too so there is no reason for this whole noble high road of romantic justice for the sake of tropes and plot. i dont mind power trips and diving into passions but you also got to enjoy the little things to which is kinda why he joined milly in the first place, to go on an adventure. plus to dangle harem and romcom tropes all over this is even more frustrating. otherwise its a pretty good series it just seems like mangaka either cant or wont write romance into their isekai/reincarnation stories instead opting for the shounen route (like this, a straight craving for power and the quest to get it) or typical isekai crap there are exceptions of course. if there is romance there is usually something very shitty about the story like himekishi ga classmate or maou no hajimekata otherwise a blush is usually all you get from mc.