“Pad Chief” (PAD(パット)長, Paddo-chō) was the derogatory nickname used for Sakuya Izayoi from Touhou Project. It was a simple, low-brow joke that accused the “Maid Chief” (メイド長, Meido-chō) of using breast pads in Touhou Suimusou, ignoring the concept of artistic liberties.

During the early 2000s, people joked that Sakuya used breast pads to explain her inconsistent breast size between Touhou Suimusou and the mainline games. The truth is that “Alphes” and “ZUN” aren't the same artist, but the people on bulletin boards simply ran with it. Due to the joke's simplicity, fan artists could easily use this as a cheap gag or push a “breast envy” theory and possibly emphasize femininity.

On the other hand, it quickly became an overdone joke as people spammed it everywhere, without reading the room,¹⁾ so most people collectively grew to hate it. Fortunately, the joke started dying out by 2009 as people moved onto propping up a rivalry with Sanae after she became a player character with the release of Touhou Shinreibyou in 2011, or moved onto generally horny trends.

The obvious antithesis would be the “Busty Chief” (巨乳長, Kyonyū-chō), insisting that Sakuya's breasts are authentic despite the art style change, though this obviously veers into adult-oriented sexual elements as busty maids are a common fetish and she'd have to disprove the claims somehow. Some people would claim, through delusion or otherwise, that you can see where her nipples protrude in the original.

For synthesis, the “Sarashi Chief” (サラシ長, Sarashi-chō) theory proposes that Sakuya binds her chest for confrontational scenarios (e.g. Touhou Koumakyou, Touhou Youyoumu, Touhou Eiyashou), but lets them loose when encountered in casual scenarios as she probably wasn't expecting to fight at a casual banquet in Touhou Suimusou. Alternatively, her breasts are just that massive.

• Considering that Sakuya is often called “perfect and elegant” (完全で瀟洒, kanzen de shousha), several backronyms playing around with this descriptor would emerge. This includes: “perfect and delicate”, “perfect and dashing”, “perfect and dainty”, “perfect and delectable”, and so forth.
• On August 11, 2007, the Nae-Radi DNA Special before Comiket 72 with ZUN, the subject of Sakuya's breast size had actually came up, but ZUN ended up dodging the question.²⁾
• Long after it had been phased out, the English-speaking community has invented a semi-serious headcanon that Sakuya is a transgender woman, having to rely on padding her chest until Eientei set up shop in Gensokyo, following the events of Touhou Eiyashou, and provided the medicine.

• Meiling's Name

• Pad Chief on Pixiv Encyclopedia
• Pad Chief on Niconico Encyclopedia