Kaamos, also known as the Kaamos Curse or Curse of Kaamos is a recurring status effect in the Boktai series that causes Django to become blue while disabling his ability to recharge energy via the sun's rays, may it be by standing outside or by doing a quick refill.
Boktai: The Sun is in Your Hand
In Boktai: The Sun is in Your Hand the curse is gained in the Abyss. After defeating the trap, at the end of the dungeon will be a small room with a green chest, when you open it, a drop of water with dark matter will fall on top of Django. Carmilla will appear to explain the Kaamos curse to Django, when leaving the dungeon, Sabata will appear expressing his preoccupation and Otenko will tell Django that he can cure himself from the curse with the Solar Tree's Morning Dew.
If a Tonniar .rm item is held while under the effects of the Curse of Kaamos, the item will turn into a Mr. Rainnot.
Additionally, the drop of dark matter will not fall from the ceiling if the sun gauge is at max.
Boktai 2: Solar Boy Django
In Boktai 2: Solar Boy Django, the rain water around the city of San Miguel is contaminated with dark matter, causing Django to become cursed with Kaamos if left to roam in the rain for too long.
While the Kaamos curse shares its original disadvantages, it grants Django a permanent sunscreen effect that allows him to use Black Django under sunlight, being beneficial for those that are familiar with Django's vampire form. The curse can be lifted by consuming a Drop of Sun or by the Solar Tree's Morning Dew.
Boktai 3: Sabata's Counterattack
Kaamos can be easily cleanse by a Solar Trance transformation.
Trivia
"Kaamos" is the Finnish word for polar night, the night lasting more than 24 hours inside the polar circles. This fits the description of the Kaamos curse perfectly; a night lasting 24 hours.