From Game Developer Research Institute
- RE: OAKS -- My best guess is that OAKS was initially a publishing spinoff of Zerosystem. OAKS was established in November 2000 and for the first few years of its existence listed the same fax number and Ikebukuro address on their corporate profile as Zerosystem. Earlier PrincessSoft releases (thorough early 2003) say "Published & Developed by Zerosystem" on the package, which was later changed to "Published & Developed by OAKS" even on titles that Zerosystem claim on their works list. Conversely, OAKS listed PrincessSoft as a publishing brand even when the packages still listed Zerosystem as a publisher.
- OAKS moved to a different address in Chiyoda-ku around 2003, while Zerosystem moved to Bunkyo-ku. PrincessSoft releases after this point only credit OAKS and list the Chiyoda-ku address. Zerosystem's site lists PrincessSoft titles through October 2003 as "published by our company". No PrincessSoft titles after this point show up on Zerosystem's works lists, and while available credits suggest the development staff was the same, Takao Ike himself is conspicuously absent from those that I've looked at.
- Both Zerosystem and OAKS stopped updating their websites in 2008. The last PrincessSoft release was in early 2009. Presumably both companies went under around this time.
- RE: Crest Works -- the known staff had previously been at Zerosystem around 1998, though I'm not certain if they were still there when they worked on Orphen or were working freelance or at another company by that point. Zerosystem's rather extensive client list doesn't include Kadokawa, ESP, or Shade so it's likely they'd already left by this point.
- Clients list (2000-2003): SCEI, ASCII, Increment P, Media Rings, KSS, Shoeisha, Media Works, Sunsoft, Sega, Right Stuff, Sugeiya; (2008): SCEI, Media Works, Black Jack, Gainax, Sega, Pao, Office Korokoro, Comic Tactics; Note that OAKS/PrincessSoft is never specifically mentioned apart from as the publisher of specific titles on the older works page.
- Some online sources link Takao Ike to other companies including Netomo (ネトモ株式会社) and Game Yarou (ゲームヤロウ株式会社), though I haven't been able to confirm this. Additionally, I've also seen eroge labels System Rose (システムロゼ) and Sakurazuki (桜月) linked to Zerosystem, also unconfirmed.