additional details: I don't know the exact cause but I got pissed at my yukkuri for shitting out so many offspring so I started kicking them, Cirno who was innocent got kicked as well by accident, I put her aside and gave her food and stuff to make her better and the she just went to sleep and didn't wake up and then that sad music started playing indicating that she took it easy forever, which is strange because I haven't killed a Koyukkuri without smashing it, burning it, or flushing it down the toilet. So Cirno was the first to die peacefully without becoming an adult.
After these events transpired I immediately left to look for a replacement Cirno.