Reminder: this is a fluffy, slice-of-life manga about a man and robot becoming husband and wife.
All jokes aside, I notice that japanese media has much less interest, generally, in keeping its tone consistent. I'm thinking in particular of stuff like Elfen Lied, which combined romcom hijinks with scenes of little girls getting their limbs torn off, or A Certain Magical Index/A Certain Scientific Railgun, which is sometimes a light comedy, and sometimes about a massive government conspiracy running Unit 731-like horrors on people. It makes walking into a new manga sometimes... unsettling. You never know when it's going to turn real dark, real fast.