Believer in Chinese / Japanese...

信徒 is the Chinese, Japanese Kanji, and old Korean Hanja word for “believer.”

Just as in English, this word can be used for a follower of virtually any religion.

This word can also be translated into English as layman, adherent, follower, laity, disciple, or devotee.

日蓮 is the title Nichiren.

This title refers to a Buddhist priest who lived from 1222 to 1282. He is the founder of the Nichiren sect of Buddhism.
According to historical documents, the Nichiren sect was established in 1252. Adding the character 宗 for sect, this would be 日蓮宗 (Nichiren sect), which is also known as the 法華宗 or Lotus sect.

According to Soothill-Hodous...
Nichiren's chief tenets are the three great mysteries 三大祕法, representing the trikāya:
1. 本尊 or chief object of worship, being the great maṇḍala of the worlds of the ten directions, or universe, i.e., the body or nirmāṇakāya of Buddha.
2. 題目 the title of the Lotus Sutra 妙法蓮華經 Myo-ho-ren-ge-kyo, preceded by Namo, or “Adoration to the scripture of the lotus of the wonderful law,” for it is Buddha's spiritual body.
3. 戒壇 the altar of the law, which is also the title of the Lotus as above; the believer, wherever he is, dwells in the Pure-land of calm light 寂光淨土, the saṃbhogakāya.