In the winter, a song can be heard from the forest.
This is a baby Kotatsu Shell Marisa. Kotatsu Marisa is a mutation of Shell Marisa, which has different accessories from the common Marisa. Kotatsu Marisa have something like kotatsu. A blanket cover almost all of her body and above it is a table, complete with small orb of orange.
This accessories completely protect Marisa from heat loss while the inside generates heat. Thanks to that, she's just fine even in this winter.
Marisa said she's being independent and going to live on her own. It's more like running away from home actually. Kotatsu Marisa has a very strong independent spirit so they usually get out from home in very early age.
There's a theory about kotatsu Marisa's origin. As we know, having children in winter is a stupid act of suicide for yukkuri. But there's many case where the yukkuri tried to fool themselves, saying they're trying to avoid cold or lonelyness through doing "rub rub" body contact.
To survive the winter, some babies then grow into Kotatsu Marisa.
As mentioned before, Kotatsu Marisa's template is an independent spirit. This way they will get out of their family's home and thus reducing the mouth to feed so their family will survive. Of course they never realize this.
Another special treat of Kotatsu Marisa is a very positive attitude. This helps them survive without getting depressed by lonelyness. Well, part of it is because they're newborn so everything in the world is new for them.
Kotatsu Marisa live alone, and they can't move actively like common Marisa. Because of that, they love to sing.
This Kotatsu Marisa has been feeding happily on soil of rotten leaves. The taste is actually not that tasty, but it's nutritious so Marisa managed to survive.
They have a very efficient digestion. Even though they eat a lot, they almost never excrete. The extra nutrition they got turns into small orange-like orb on the table. Many well feed Kotatsu Marisa can grow 3-5 oranges. Those even better feeded would also grow a hot cup on the table.
A Cirno greeted Marisa.
Another purpose of singing is to gather friends. No matter how positive they are, Kotatsu Marisa still enjoy company from friends. Because of that, they sing to gather other yukkuri.
In the other hand, Cirno types usually kept distance from other yukkuri. They need friends who doesn't mind cold.
One month later, they have another new friend. This is the predator Letty type. Usually Letty type eats Reimu and Marisa type, but Kotatsu Marisa is an exception.
There's still no aggreeable explanation. A theory said that Letty type also feel lonely and need friend. Another theory said that the kotatsu accessories doesn't look tasty.
Kotatsu Marisa's growth is very slow. This one hasn't grow more than orange size. She also still has the baby slurring in her words. Academic world theorize that this is because their internal heat generating ability consume a lot of energy, while their metabolism is also very low.
Because of this slow growth, it would take two years for Kotatsu Marisa to grow into an adult yukkuri.
As spring approaches, the season of winter yukkuri will ends.
This Letty is not eating other yukkuri. During the spring until autumn, Letty sleep in a cave while the nearby clan make use of the cold wave produced by Letty to preserve their food. There's also this kind of relationship between Letty and common yukkuri clan.
Kotatsu Marisa is weak against heat. Moreover, their accessories can't protect them from heavy rain and typhoon. By instinct, they usually hibernate together with Letty or Cirno types, making use of the cold wave.
When preparing to sleep, a Dosu Marisa approaches. This Dosu is the clan's sub-leader. She ask about the weird Marisa and Lety told her that Kotatsu Marisa is her friend and she want to ask leader to let Marisa join the clan.
Marisa retracts completely into her kotatsu and both fell asleep until next winter.