Well my yaoi friend- I can't help you much but here is the author/artist to Kijima-kun and a list of their work at the bottom- good luck finding! https://www.mangaupdates.com/authors.html?id=1163
wel...
https://www.mangaupdates.com/series.html?id=97582
With Related Series says it 'N/A'
so this means that there is none right...?
I don't know (': to be honest this is confusing me as well and i tried to find what they were talking about but I couldn't come across anything ;-;
I think the brother's lover shows up later on in this series
But it says clearly 'in others series'...
I know. But if you look at where the volume titles are listed, volume 9 should be about the brother, plus he's the one on the cover...so that's where my guess is coming from :/
Maybe the person said "other series" because they see it as a separate story?
http://www.mangago.zone/read-manga/kijima_kun/mf/tr_chapter-7.5/pg-19/
Where it says with the picture 'looks like subaru's brother's lover, in others series' ???