So the "taking the marble out without breaking the bottle" metaphor I interpret it as Kamachi wanting more of an intimate relationship with Suzu, but fears that if Suzu finds out Kamachi likes him it would ruin their friendship and Suzu might reject him: http://www.mangago.zone/read-manga/ramune_no_shalala/mi/504c0bc46b11695a2a3a1374702d023f_chapter-1/18/
They look like the creepy male versions of the twins from The Shining, lol: http://www.mangago.zone/read-manga/geu_kkeute_issneun_geos/uu/geu_kkeute_issneun_geos-chapter-33/34/
This has to be one of my favorite yuri couples, they're so adorable and have so much chemistry, it's crazy. It has the same characters of another one-shot called "From Aiu Station On The Hiragana Line". So you could call them two-shots xD.
"From Aiu Station On The Hiragana Line" seems to be the prequel to this one.
"Houston, we have a problem! There's a super pretty girl here! " had me roll on the floor laughing.
http://www.mangago.zone/read-manga/riko_to_haru_to_onsen_to_iruka/bt/166926/Vol1_Ch1/19/