Let’s not pretend otherwise, the plot of this doujin is as thin as they get. The author spends no pages on any convoluted setup, but rather jumps straight into showing Master filling up Mash, Scathach and Jeanne Alter’s mana reserves. Multiple times each, using different "sockets".

And all of that thanks to Scathach, who prepared both sexy outfits for the Servants and stamina boosters for Master. As expected of the experienced witch.
*All characters depicted in this work of fiction are adults, regardless of their visual representation or textual description, and are not based on any real person*