Koko wa Ima kara Rinri desu., Mystery to Iu nakare Recommendations
Reading them feels like reading a philosophy book, and that's a good thing! Both includes main character who likes to question every actions and decisions, looking at them through ethical and philosophical point of view. "There isn't a correct answer, just a long discussion" is what basically sums up most about what's inside the manga. It makes you think while reading, but in a fun way!