Chikasugiru Futari

From the moment they were born, they’ve been together through everything—waking hours, sleeping, and even bath time. At this point, calling them "childhood friends" feels a bit too soft. No, these two are "Sh**-tier Friends."
More than childhood friends, but less than lovers. Having come full circle, they're basically an old married couple.
The curtain rises on this "Sh**-tier Friend" rom-com, where the sense of personal space is completely broken!

https://www.cmoa.jp/title/360696/