Trying to find this one mango I've read many years ago. It's about some guy who's visited by a deity/goddess/familiar of some sort. She's short and has blonde/white hair, and some odd things on her face that makes her look a bit like a doll. Turns out he's not the only one who's "received" one of these familiars, and they act sort of like stands for the people they're assigned to.
Each person can make their own familiar use their special power to fight monsters by shouting a specific word or couple of words, which is determined as the first thing the person says to their familiar when they first talk to them, or something like that. After using their familiar's power, they have to "pay" a toll of some sort, like the characters from Darker Than Black; smoking, counting beans, etc.
In the MC's case, through some silly situation, his familiar's attack is activated when he shouts "GOD DAMMIT" and it explodes the target, and his "toll" is a crippling stomach ache that lasts all night long. His house also blows to smithereens at one point and the only thing left standing is his toilet.
Last thing I saw in it was the MC going out to buy things for his familiar, like her own toothbrush, alarm clock, and so on. The author went dark ever since.