While it has a number of surprisingly cute romantic comedy segments, the age-gap in Yarinaoshi Reijou wa Ryuutei Heika o Kouryakuchuu ends up impossible to look past due to how often it gets called out. It’s a very weird dynamic, a 16-year old in a 10-year old’s body and a 19-year old with a childish split-personality, that never really manages to rise above awkward. The second book in particular has some issues in that respect.
Also a romantic comedy, Watashi ga Seijo? Iie, Akuyaku Reijou desu! (which has a totally different English title) is basically what you’d get if you condensed the Higeki no Genkyou series down into a single book. Apart from the utterly bizarre vaccination focus in the first half it’s decent enough, just be forewarned that much of the comedy is based on embarrassment and/or misunderstandings.