Aoriki said: Ether Yellow had a miscarriage or she on her cycle....Yeah.
It would appear to be her first menstrual cycle. Judging by the first part (I never saw it on here, so on pixiv - http://bit.ly/VZHWVV ), and Red's behavior towards having a wetdream about Yellow ("I... might like a guy"), it's also before he realizes she's a girl.
Also, without the first-part, reading Green's call to Blue gives enough context to explain what happened. If it was a miscarriage, they'd sooner go to a hospital than have something bought/brought over -u-
No need to worry, then...Yellow!Where are you?!Re-RedIBlood...It won't stop...!!The blood...Butah ah!All of a sudden!It's all right......if I drink more milk, it would be trouble some...Well, I still can see quite well down there...Come on, come on, heave-oh!It'll be over quickly....you're doing it anyway...Even if I told you to stop!You wanted to measure me only there...?Yeah, thanks.hmm...As expected!We're next!ChuChu and the others said it's alright, but...to find a cure for you!Absolutely...!!shockAre you inside!?shockIt hurts!I'm scared!...I...I'm ill or something, right?It's all right.I would travel the whole country...no, the whole world...Thank you, Green!chu?Even if you were ill......gh...R-Red! I believe you and I'll wait for you!stare~Hey.umyu~Can I take your measures?And stop pushing me down, you're heavy!Don't worry, but calm down now.grabYes! I'll find it for sure!Blue? Sorry for coming out of the blue, but there's something I'd like you to buy me.Before that idiot sets out, please.End.Bonus Ruby x SapphiremutterAs I thought, they're grown 3mm. since the last time, your breasts....Ruby...Give me that notebook RIGHT NOW!Unintentional flirting, just a bit sexual harassment - Ruby x SapphireOne day I'll draw it...It's not! Not yet!You're too quick-tempered, Gold!!WHAT!?Yeah, quickly.chu~Are you alright?!Yellow!chu~chu.Sapphire...I'll burn it!
