List of PC-98 References in Undefined Fantastic Object
Put it like this: ZUN is either the Touhou fanbase's biggest troll, or he rolled a critical failure on an "appease the PC-98 fans" check. You may assume that this is going to have spoilers. (Disclaimer: my PC-98 lore is relatively low, in part due to never having played Phantasmagoria of Dim.Dream (and thus information from that direction will be secondhand), so feel free to suggest additions.)
- The first thing any PC-98 fan would think of upon seeing "UFOs" and "flying ship" in the context of Touhou is the Probability Hyperspace Vessel belonging to Yumemi Okazaki from Phantasmagoria of Dim.Dream.
- The silhouette on the cover of the CD jewel case superficially resembles Yumemi, as well. Fans were quick to point out that the silhouette apparently wore a cape.
- The Stage 4 and 6 midboss is an invulnerable blue ball of light (Nue Houjuu in disguise), bearing a marked resemblance to a similar enemy near in the Extra Stage of Lotus Land Story.
- CAPTAIN MURASA is basically Chiyuri Kitashirakawa from Phantasmagoria of Dim.Dream except with black hair and a huge anchor. She also shares a teleportation move Chiyuri has in her EX-attack.
- Luize, as the stage 4 mid-boss in Mystic Square, also has a similar teleportation ability.
- Stage 5 and 6 take place in Makai, the setting of most of Mystic Square and of the last two stages in Story of Eastern Wonderland.
- ZUN's notes in Mystic Square's music room regarding the track "World's End," the Final Stage theme, mention that he "wanted to do it with just a heartbeat sound"; the first thirteen or so seconds of "Fires of Hokkai," Undefined Fantastic Object's Final Stage theme, are ... silent except for a heartbeat sound, which is audible throughout!
- Byakuren Hijiri's Spell Card Great Magic 「Devil's Recitation」 is basically Shinki's final danmaku pattern.
Why PC-98 were reacting badly
The PC-98 fans want the return of the PC-98 characters. This has already happened with Yuka Kazami and Alice Margatroid, and in the latter case she's become so established in the modern canon that she's seen as almost as much a Windows character as, say, Hong Meiling or Yuyuko Saigyouji. So why not bring more characters back? Nor are these fans strangers to disappointment, either: including spinoffs and fighting games, there have been a total of four Touhou games released between PoFV (the last game to reintroduce a PC-98 character) and UFO.
So what happened?
What happened was that ZUN gave an implicit "I have not forgotten the PC-98 games or the characters in them. I just don't feel any need to directly bring them back."
The PC-98 fans interpreted it as, "I haven't forgotten the PC-98 characters, and I know you want me to bring them back, but I'm just not gonna," and took it personally.
Of course, now all forms of hype and RAGE have died down for a bit, but that's where we are now.