d4 pl4n = the plan
"mr. Piro-san" is not a goofup, for the 10,000th time.
Yuki wrote "Mr. Piro-san" (Mr. ぴろさん) quite literally. In something like this you cant really show mixed english and japanese very well without confusing people, but Yuki throws in english words here and there as she writes. the akward sound of 'Mr. Piro-san' is deliberate.
Random note: Mr. Building = Mr. Biru = Mr. Bill.
(Mr. Bill is a clay figure from Saturday Night Live who would scream OH NOOOOOO before getting smashed. The closest you can get to "Bill" in Japanese is "Biru", which is also a Japanese word for building.)