This director likely has a pseudonym from his past AV work. In the description of his first pink film, "Toshiyuki Ueki, who started out in the AV industry, is making his film directorial debut" (AV出身でこれが映画初監督となった植木俊幸が.

Contenders for his "AV" past: Most likely: 金子真一郎

• This AV actor appears in the director's second film, according to the actor's Wikipedia. Perhaps same person?)
• If correct, Shinichiro Kaneko (金子真一郎) met Kiyomi Ito on a 1993 "Groper Train" (痴漢電車　いやらしい行為) before he directed & she wrote his second pink film (also a "Groper Train").
• Shinichiro Kaneko started an AV company (in 1994) and worked as an AD after that. This likely gave him the directing experience for his 2 pink films.
• If this helps, his AV name was 観念絵夢
• Further info: 観念絵夢 is credited.

植木吉太郎 (shares 植木 family name)