After defeating the Basilisk, the protagonist can teleport to an isle in the Expanse. On said isle, a naga is impaled by the Kuchinawa Sword. The protagonist then helps him by using Amitabha's Might to extract the sword. The naga joins the heroes and gives the blade to them.
"Snake gods of Indian mythology. They are usually depicted as human from the waist up and snake from the waist down. They are regarded as gods of the harvest, fertility, and reincarnation. Their venom can kill with one strike, and their bodies are immortal and can heal from any wound. Female Nagas are called nagini and are said to be both beautiful and clever. The Nagas possess many of the world's finest jewels, which they use to illuminate the underground palaces in which they dwell. Because of their awesome defensive powers, statues of Nagas are often placed at the entrances of temples."
—Shin Megami Tensei IMAGINE compendium
Naga can be contracted within Shinjuku Babel's docks area. A particular floor in the Denshi Kairo instance has a constant respawn of Naga that can only be passed by summoning a Garuda.
"Half-snake, half-human, they are divine beings in Hindu lore. Worshipped as bringers of fertility. They live in the bottoms of lakes and seas, and enjoy singing and dancing when they are not fighting."
Two Naga appear in a mini-boss battle once Flynn enters the 3rd stratum of Naraku. A hooded figure will summon them in an attempt to teach Flynn that there are limits a casualry can't overcome by exerting themself.
Naga can later be encountered in the areas surrounding Ueno on the world map. He can teach Flynn the Lunge, Bufu and Tarukaja skills through his Demon Whisper. Naga is one of the demons needed to summon David through special fusion.
Naga can be found in the Toyosu Shelter and in the Konganji Passage in Ginza. He can teach Nanashi the Head Crush, Bufula, Tarukaja and Fatal Sword skills with his Demon Whisper. Naga benefits from learning Physical and Ice skills.
"Half-snake, half-human divine beings in Hindu lore, worshipped as bringers of rain. They live in the bottoms of lakes and seas, singing and dancing when they are not fighting."
—Persona 5 background
Naga is the fifth Persona of the Hermit Arcana and can be found as a Shadow in Futaba's Palace and the Akzeriyyuth area of Mementos, with the title "Cavern Snakeman." Naga is the first Persona that the protagonist can use in battle that learns the Zionga skill and is the first of four Personas to learn Elec Boost. Naga is also the first Persona to learn the Mazionga and Marakukaja skills. When itemized through Electric Chair execution in the Velvet Room, Naga yields an Elec Boost skill card. Naga is one of the Personas required to summon Vasuki through advanced fusion.
Upon entering the power plant, the party will come across a couple of Karma Soldiers smashing the consoles which open the main doors allowing access to the deeper parts of the facility. They will transform into Naga to engage the party. They will also be encountered in random battles in the area. In the boss battle against Raja Naga, he will summon reinforcement of Nagas infinitely to ensure there are always 2 Nagas fighting alongside him.
"Snake gods of Indian mythology, depicted as being half-snake and half-human. They are regarded as gods of rebirth or reincarnation. The Naga live at the bottom of lakes, in rivers and oceans. When they are not at war, they live a joyful life singing and dancing."