There are two answers. A person who practises a healing method is a reiyōshi. But the memorial stone of Mikao Usui describes him as someone who undertook shugyō, committed training, and a person on that path is a shugyōsha. From a Japanese perspective that is the better word for a Reiki practitioner: someone committed to daily self-practice, not someone with a certificate.

Chakras came into Western Reiki from the New Age movement and have nothing to do with the Japanese system. Teaching from a Japanese perspective, I work instead with Sanmitsu, which I call the Three Diamonds: body, mind, and the breath that links them. Those three sit at the base of every practice in the system.