"Eromanga Sensei" volume 12 by Fushimi Tsukasa. This volume features Elf's mother.
A notable event in this volume is that Sagiri has ventured away from the house than ever before, unfortunately I have recently read another novel that made a big deal out of recovering from social withdrawal, so Sagiri's accomplishment here seemed relatively weak. But actually the real notable part of why Sagiri did it, and this has to do with Elf's mother.
The subtitle of this volume is "Yamada Elf-chan's Reversal Victory", one possible plot that might fit is to have Elf's mother show up and threaten to take Elf away from Japan, Masamune would then intervene and in the process realize how much he likes Elf. The actual sequence of events is not too different, except the last bit ends with Elf's mother saying "Emily, you should break up with this man... this kind of man will not change his heart". This is exactly the outcome I expected, but perhaps this best part about this series is about giving readers very much what they expected without any surprises. It's best summarized by the dialog between Masamune and Elf: "this is the apex of Izumi Masamune! This is what I wanted to write the most!" "But it's one-pattern."
There is one bit of surprise that didn't fit the one-pattern mould, and that has to do with Elf's victory criteria -- Unlike most other series where the ending is where two persons form a couple, Elf defined success as a polyamorous relationship among the three characters. This is a fairly bold concept.
Other than Elf's bold proposal, this volume is very much what I expected, following the "defeat new boss who then becomes friend" formula as mentioned in volume 4. Can't say there is much progress but it has been a pleasant read.
Previous (2020-02-19): "Seishun Butayarou wa Odekake Shisutaa no Yume wo Minai" by Kamoshida Hajime
Next (2020-03-11): "Imouto sae Ireba Ii" volume 13 by Hirasaka Yomi