Woof Woof Story: I Told You to Turn Me Into a Pampered Pooch, Not Fenrir! (Light Novel), Vol. 4

We all knew this day would come... Routa's pampered pooch life has finally caused him to grow too big to comfortably fit in the mansion! Resolving to go on a diet, he heads to the forest to see if the elves can help him out. And, surprisingly, adventure finds him ready and willing! But no matter how eager Routa may be this time around, he probably wasn't expecting Lady Mary to show up on the enemy roster!