So i vaguely remember something. It's not Hoshi no Yakata but it's the same toy from one of the chapters.

So there are 3 people. Two are strapped down or something and the third is the seme. The seme/third person has a toy which is...a two sided dildo? I guess...something like that. Well he puts one side in one of the guys strapped down, and make the other one push it into himself...well. It causes the other side to be pushed into the other guys.

I think the ukes were brothers? cousins? well they were somehow blood related or something.

I know it's not much but I hope you guys can help!

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There's an old saying my late grandma taught me. When you're ten, they call you prodigy. When you're fifteen, they call you a genius. Once you hit twenty, you're just an ordinary person. About three years until I'm ordinary. Man... I can't wait to be ordinary.

The only yaoi I read with a scene like that was Kinpeibai Kinden Honoo no Kuchizuke, but from your description the story is different, the two uke are not blood related.
I'm curious to know the title too

It's similar but I don't think that's it. Thanks anyways! It was a good read!

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There's an old saying my late grandma taught me. When you're ten, they call you prodigy. When you're fifteen, they call you a genius. Once you hit twenty, you're just an ordinary person. About three years until I'm ordinary. Man... I can't wait to be ordinary.