All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
It is impermissible to wear that amulet or necklace (the Magatama beads) given the authentic hadeeth indicating the prohibition of wearing amulets and that it is an act of Shirk (associating partners with Allah). The Prophet, sallallahu ‘alayhi wa sallam, said, "Whoever wears an amulet has committed Shirk." [Ahmad and others] Also, there are authentic ahaadeeth underlining the prohibition of imitating the disbelievers; the Prophet, sallallahu ‘alayhi wa sallam, said, "He is not one of us who imitates other than us..." [At-Tirmithi]
We have come to know that the Magatama beads are curved, comma-shaped beads made of agate, quartz, or the like as a symbol for Shinto (the ethnic religion of Japan) and Taoism (a religious or philosophical tradition of Chinese origin). They are worn as an accessory in addition to their religious significance as offerings to their so-called gods or for good luck or protection. They may also be considered a rosary (prayer beads) to them. Such an item is prohibited for Muslims to wear because it is a symbol for a false religion and an amulet, and because wearing it involves imitation of the disbelievers.
Allah knows best.