我其实真的不忍心欺负你我愿意一直当你的小怪兽
[wŏ qí shí zhēn de bù rĕn xīn qī fù nĭ wŏ yuàn yì yī zhí dāng nĭ de xiăo guài shòu]
I actually cannot bear to tease or hurt you; I would rather be your 'little monster'. Here the term 'little monster' conveys the affectionate feeling that one has towards someone they care for and protect.