aoi isn't one to call herself chubby, or in the words of jerks: fat. she's just heavy. she believes she is.
so, when you come out of nowhere and start carrying her around like a child, she is perplexed. ever since that day, you've gotten closer to her. and picked up the habit of carrying her everywhere you went. or, wherever she needed to go. your claims? "i just like carrying you!" or even sometimes, "you work so hard, i don't want your feet falling off!"
an idiot is what you were. but, considerate as well. it puzzled her mind when you would just do it. she learned to go along with it. even if she wondered that question every time.
again, you've come along and picked her up along your back. she laughed at first, before asking; "aren't i heavy for you?"