Well, I found the introduction of lesbian characters in 50 x 50 and Sumanai!! Masumi-kun very refreshing. Women in BL are often portrayed as meddlers and annoyances (a whole issue unto itself), but in these particular series, women were positive characters. Perhaps because they were lesbians, they were not seen as "threats." 🤨

Are there any other BL mangas depicting f/f couples alongside m/m couples?

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Reading: Kingdom, Sangokushi, Historie

Wedding Bells its yuri not yaoi, but its got both kinds of homosexual, though it mainly focuses on the girls.. its as close as I can get to what you're looking for.

Feed your head.

You might want to check out works by Eiki Eiki. She does both BL and GL, and there is some overlap. Not sure about Zaou Taishi, but they do collaborate a lot, so her works might be worth a quick look, too.

No out-and-out lesbianism here, but Koicha no Osahou has rather subtext-heavy extras portraying the sisters of the main pair.

Makeinu no Nandemoya
The Imitation Lovers
Complex (volume 2 chapters 4-6?)
Loveless (end of volume 3, volume 4)
Lovers' Kisses (has BL, yuri, and het)
Kaguya Hime (has BL, yuri, and het)
Unmei ni Kiss (chapter 4)
Gamen no Kokuhaku (see http://yurizuki.net/gamen.html)
Sex Pistols (chapter 17)
Furachi na Bokura
Tomoi
C!! (4-panel strips about a group of women that draw yaoi doujinshi; see http://yurizuki.net/c.html)
HEN: Suzuki & Satou (I think the yuri couple from HEN also appears here)
The covers of Princess Princess (under the jacket) have "Prince Prince" yuri gags

Haru ni Nareba Kusa no Ame by YOSHIKAWA Utata

Some of these are couples, and some are unrequited love.

There's the nice OEL Honeydew Syndrome, which has some pretty awesome lesbians.

Thank you! There are a lot of mangas here I wouldn't have thought to look at.

Avatar by tassyn.livejournal.com

Reading: Kingdom, Sangokushi, Historie