The Great Monsoon

Background
In the year 2861 AD, a rouge glacial comet collided with the volcanic planet Fernos. The initial impact caused domino effect starting with a planet wide quake, that caused volcanic eruptions. The volcanic eruptions near the glacial comet caused a violent reaction of steam. This steam created a hole in the atmosphere. As the steam cooled, it turned to rain, the temperature of the planet dropped, and many lives were lost as a consequence. Forunately, the comet's impact shifted Fernos' orbit closer towards its sun. This over time made the planet's temperature rise, eventually everything returned to normal, except the Onibi's way of life.

Year 2861 AD
Towards the start of the year, a rouge glacial comet collied with Fernos. It is rumoured that 2000+ were killed instantly with another 4000 injured the initial burst of steam rose up and ripped a hole in the atmosphere allowing cosmic radiation into the planet. This steam and the frozen comet caused massive eruptions following shortly and last many months prior. The comet's impact caused a quake which was felt upon the other side of the planet, triggering eruptions that side of the planet.

Year 2862 AD:
It wasn't until the second year that the rains started. These rains continued right up until the end of 2863. It was the unexpected first downpour which had the highest casualty count, in the millions. With millions more injured and eventually dying from their injuries, the only safe place left on Fernos was underground, yet with the temperamental nature of the planet there was no where safe definitely.

Year 2863 AD:
By the end of the third year, the planets temperature started rising, causing the rains to stop and the eruptions less frequent and more predictable. The Onibi learned to adapt to and have now abandoned a highly developed civilisation in favour of a more natural way of life. They'll never forget the events during the great monsoon, nor will they forget the events that followed and climaxed with the steam war.