Looking for a forgotten SoL/mystery manga

[DjAlexDubCheck]

Some years ago I read and enjoyed a Slice of life crossover series.
It's set in contemporary Japan, featuring a teenager and his older MtF transgender sister
trying to solve a mystery about the island they live in (some people disappearing IIRC).
It managed to have a nice laidback atmosphere despite its disquieting premise.
I'd love to read it again but can't remember its name or author unfortunately:
any help or clue will be appreciated

 

[undeed]

slice of life, mystery, siblings, transgender...
that points me to Reiwa no Dara-san
but that series is new

 

[DjAlexDubCheck]

slice of life, mystery, siblings, transgender...
that points me to Reiwa no Dara-san
but that series is new

Some elements overlap indeed but there aren't small islands in Dara-san

 

[Yatsuki]

@DjAlexDubCheck I'm really sorry in advance if you find the barrage of questions annoying.

Can you explain the "crossover" aspect?

Did you read this series on mangadex, any other sites (especially if it's a site that allows official releases like bato), or published paper book? And in English or local language? Was the series completed?

Also can you remember anything else about it. Example: the beginning of the manga? The characters personality or any other outstanding traits? Aside from MtF sister that you already mentioned of course.

 

[DjAlexDubCheck]

@DjAlexDubCheck I'm really sorry in advance if you find the barrage of questions annoying.

Can you explain the "crossover" aspect?

Did you read this series on mangadex, any other sites (especially if it's a site that allows official releases like bato), or published paper book? And in English or local language? Was the series completed?

Also can you remember anything else about it. Example: the beginning of the manga? The characters personality or any other outstanding traits? Aside from MtF sister that you already mentioned of course.

a) Crossover between slice of life and mystery genres
b) It's here on Mangadex, completed in English (it wasn't very long, one volume or two at at the most);
possibly in my library too but it's hard to navigate (devs should make it readable in alphabetical order at least)
c) Can't remember other particularly outstanding traits at the moment

Thanks for the assistance