hold up, we're supposed to believe the MC didn't connect the dots on them being the same age and their birthday being 5 months apart? the hell is up with that
Man, that's taking the trope too far. The MC is capable of create a plan to catch the "culprit" but is incapable of basic subtraction. Same age and just five months apart? Give me a break.
At this point I have to lean on the belief that the MC is a beta. Expecting anything but a pervert from a girl who left you panties with a love letter was stupid from the start. The story should shift to him accepting his perverted harem otherwise there is zero reason to continue because there is no story.