Day 30 covers all of Chapter 26, Dhāraṇīs

Having last month heard the dharani spells of Brave-In-Giving Bodhisattva, we come to Vaisravana Heavenly-King.

Thereupon Vaisravana Heavenly-King, the Protector of the World, said to the Buddha, ‘World-Honored One! I also will utter dharanis in order to protect this teacher of the Dharma out of my compassion towards all living beings.’

Then he uttered spells, ‘Ari, nari, tonari, anaro, nabi, kunabi.’

[He said to the Buddha:]

‘World-Honored One! I will protect this teacher of the Dharma with these divine spells. I also will protect the person who keeps this sutra so that he may have no trouble within a hundred yojanas’ distance [from here].’

Lotus World offers this about Vaishravana, whom Nichiren placed in the upper left corner of the Mandala Gohonzon.

Vaishravana is the chief of the four heavenly kings. The Flammarion Iconographic Guide: Buddhism describes Vaishravana as follows: Vaisravana is the guardian of the north and the chief of the four guardian kings, ‘He who is knowing’, ‘He who hears everything in the kingdom’, the protector of the state par excellence, sometimes thought to be a god of defensive warfare. In China, he is considered to be a Buddhicization of the Indian god of wealth, Kuvera, the north being considered to hold fabulous treasures. He presides over winter and is black, so is also called ‘the black warrior’. His symbols are a jewel and a serpent, and he commands a large army of Yaksas.

Vaishravana’s army and attendants consisted of the kimnaras and the yakshas, two of the eight kinds of supernatural beings who are said to revere and protect the Dharma. The kimnaras are celestial musicians and dancers who have the bodies of birds with human heads and torsos. They officiate at Vaishravana’s court. The yakshas are a kind of flesh-eating demon or spirit who make up Vaishravana’s army.
Lotus World: An Illustrated Guide to the Gohonzon