The Hakkero (八卦炉; translated as Eight Trigram Reactor or Elemental Reactor) is a magical artifact currently possessed by Marisa Kirisame. It was given to her by Rinnosuke Morichika in Curiosities of Lotus Asia. The Hakkero takes the shape of an octagonal block, made of wood, with the eight trigrams printed in a circle on its front; despite its small size (it fits easily in the hand), it is a potent source of magical energy, and Marisa uses it to power her Master Spark.
In Mountain of Faith, Marisa has Hakkeros as options.
A different sort of Hakkero appeared in the legend Journey to the West, where it was a furnace in which the monkey king Son Goku/Sun Wukong was imprisoned as punishment after devouring the peach of immortality.