Think about it: lesbianism is thought to be a normal "phase" of youth in Japanese girls; Japanese men generally don't adhere to "masculinity" as much as people in the west; homosexuality was custom in ancient Japan; the obsession for futanari, trannies, and newhalves; all the gender-bending/shotacon/BL/bara/crossdressing stuff being consumed by men; etc.
Seems like most people in Japan are homosexual, bi or pansexual, given that apparently biological sex isn't as important for men as secondary or tertiary sexual characteristics (like clothing, traits, roles, etc.), and women pretty much can have romantic and/or sexual relationships with either gender.

Dead or Alive Ero-SFM Doubly Dirty
Flying Witch “Cute But Boring…”
Goddess of 2ch “Another Bathing Beauty!”
Phantasy Star Online 2 Phantastic: “What About the West!?”
Shounen Maid “A Fujoshi Delight”