oooh, good question! i'm actually not sure QUITE how well-known these series are, but i don't hear about them too much and i liked them a lot!
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Composing Spring In This Room Where Cherry Blossoms Bloom: a woman tries to move on when her wife passes away suddenly. it's devastating, quiet, sad, and pretty, as you might imagine!
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I Don't Know Which One Is Love: a woman goes to college to find a girlfriend. she finds several. i won't spoil anything but when i recognized what was happening with the harem i screamed. horny in extremely funny way
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Yuri Espoir: a girl doomed to arranged marriage with man convinces her friend to join her lesbian-watching hobby. another yuri with an incredible conceit once it gets going. CW for exactly ONE chapter that gets ridiculously violent. ongoing!
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An Undesirable Relationship: incredible NSFW short comic. god damn, can Tamifull write some lesbians. and draw some lesbians. this is it, and you should read it. perverted in an incredible way. perfectly condensed toxic yuri.
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The Moon on a Rainy Night: wonderfully written high school yuri. the characterization is strong and the writing is interesting and human. i wrote a lot about it here if you want more details ~
..... sorry, i wrote about a bunch of them, and then saw the question said "a" series... well...