|Connects To||North Ryoshima Coast|
|Notable Inhabitant(s)||Queen Himiko
Kagu (Okamiden Only)
Miko Cho (Okamiden Only)
Dr. Bluebeard (Okamiden Only)
Veil of Mist Brush Technique
Fireburst Secret Brush Technique
Deluge Secret Brush Technique
Thunderbolt Secret Brush Technique
Sei'an City is the capital of all Nippon and it is found in Ryoshima Coast. It is separated into two parts, the Commoner's Quarters and the Aristocratic Quarters and these are linked by the Gojo Bridge. The city is located in the centre of a Lake Beewa so it has a network of canals flowing through it.
When Amaterasu and Issun first arrive in Sei'an the whole city is covered by a toxic green mist that is causing the citizens to become ill and die, the canals have also all dried up making it impossible to get to the Aristocratic Quarter.
Amaterasu first needs to solve the water crisis by helping the City Carpenter, Naguri, unblock the pipes which fill the canals by means of a Digging Mini Game. After the water has returned Amaterasu must help Benkei catch the "Living Sword" before he agrees to raise the bridge.
After Amaterasu gains access to the Aristocratic Quarter of Sei'an she still cannot banish the green mist. Instead she must explore the Sunken Ship with Rao. This will lead her to find the Lucky Mallet which can shrink her down to Issun's size allowing her to get through a crack in the wall. This crack leads her into The Emperor's Palace, which is the source of the toxic mist. After Amaterasu kills Blight who is producing the mist whilst being inside of The Emperor the city is purified again.
 Commoner's Quarters
This is the first part of Sei'an Amaterasu explores, it is also the largest part of the City. It has an Origin Mirror near the exit to Ryoshima Coast along with a Tools Merchant and a Weapon Dealer. Given the name, the city's commoners live here. The Tao Trooper's base is also found here, floating high above the buildings.
 Aristocratic Quarters
Amaterasu can visit here after she has convinced Benkei to raise the bridge, she must pass through Rao's lecture hall before she can reach it. The area is both smaller and less populated however it does have a lot of very tall houses which most of the residents never leave. It contains the Imperial Palace, which is home to the Queen of all Nippon, Himiko as well as the The Emperor's Palace. Benkei takes up a permanent Fishing near the area's Mermaid Spring. This is also Komuso's last location.
 Side Quests
After defeating Blight the citizens will start having having problems which Amaterasu can help solve for Praise and other Treasures. Most of them have some pre-requirements before you can take part in them. Below is the list of side quests found in Sei'an City:
- Ferry Service; Around the canal there will be several people standing, drawing a lily pad in front of them will cause them to hop on it. Amaterasu can then use Galestorm to blow them to their destinations but within a time limit, however she must watch out for whirlpools which will slow her down. She will get a certain amount of Praise and Yen depending on how quick she transported them.
- Inferno Brush Technique; You first need to get the Golden Mushroom from the tea house owner in Taka Pass. If you then give it to Yama in his restaurant he will tell you to draw the infinite symbol over his oven. This causes Moegami to appear and teach you Inferno.
- Wanted List; If you talk to Masu inside Yama's Restaurant at night he will ask you to complete his wanted list of monsters around Ryoshima Coast. Completing it earns Amaterasu Praise and Gold Dust.
- Kimono Design; First you must buy Charcoal from the tool dealer and give it to the little girl drawing pictures at the east of the Commoner's Quarters. Everytime you talk to her a new design will appear over her head, you should take this design and draw it on one of Mr. Chic's Kimonos. If done right he will say it might make something happen. Continue this for a few patterns and you will get a Stray Bead.
- Reviving Cherry Blossoms; First revive all of the non cursed trees in the city. Talking to Mr. Flower will let you know how many are left, the most missed ones are the ones in and on his house and the one on the head. Mr. Flower will the run around and revive all the cursed trees but you must help him Bloom them. This rewards you with lots of Praise.
- Healing the sick; First you must buy the Herbal Medicine from the Tools Merchant and have helped Mr. Flower revive all of the cherry trees. You must then give the medicine to the Blossom's Papa in the house near Mr. Chic's shop. After reviving the Cherry Trees you can headbutt him and he will leap out of bed, cured from his illness. He will not leave before this as he refuses to without the cherry trees being in bloom.
- Stopping the thief; First you need to light the large light nearby whether by visiting the Tao Troopers or using Thunderbolt. At night you must chase Hayazo out of his hiding place, usually a rock, and chase him around the city. He will split into a few people and each one must be taken down in the proper order using the correct techniques. Defeating him will cause him to drop and item which you must return to it's owner for Praise. However if he is not defeated by morning he will disappear again till night.
- Deluge Brush Technique; After you return from Oni Island you can use Waterspout to sprinkle water on Himiko's Grave. This causes Nuregami to appear and grant you a Secret Brush Technique.
- Belief in the Gods; First you must get Camille and Camellia to leave Kamiki Village and learn Deluge. You then must make a tree appear in front of Camille by dotting the ground and follow it up with Deluge. This earns you Praise and Camille's belief in the Gods.
- Thunderbolt Brush Technique; You must get the Gimmick Gear from Ida and give it to Gen who can be found in the Aristocratic Quarter. Then draw the Thunderbolt symbol on Gen's invention as this will cause Gekigami to appear and teach you the secret Brush Technique of Thunderbolt.
Sei'an City makes a reappearance in Okamiden. When Chibiterasu first arrives there, after defeating the Catfish boss in Agata Forest, something feels off about it. There are Demons tormenting the citizens and many houses are possessed or simply abandoned. Chibiterasu ends up partnering up with Kagu and they explore her parent's Playhouse, where she is a famous actress. After they do battle with Sen, Ryo and the possessed puppet Renjishi the demons are frightened off. It is then up to Kagu and Chibiterasu to purify the possessed houses.
When Kagu leaves for her Miko training in the Imperial Palace, it is in Sei'an City that Chibiterasu partners up with Kurow to explore the Moon Tribe Ruins. King Fury then lays a curse on the city and it is up to Chibiterasu and Kurow to free the city and rescue Kagu from his possession. Kurow and Chibiterasu must return to Sei'an City after King Fury's defeat in order to meet Gen and use his time machine to follow Akuro back into the past.
Many minor characters from Okami can be seen wandering around the streets such as the Samurai Dandy and Momotaro and others such as Blossom and her Father are mentioned, although their houses are boarded up. Reappearing characters with slightly larger roles include Mr Chic, Yama and Mr. Flower, whose cherry blossoms have also been cursed.
It is also in Sei'an City that a Manifest from the Ruin Explorers can be obtained, all of their missing journals can be found in the ruins. This is obtained outside of Rao's now abandoned office. Chibiterasu also obtains the Devout Beads on the Gojo Bridge.
Sei'an City is home to many future Migrants to Yakushi Village.
Sei'an City is based off Heian-kyo, which eventually grew into modern Kyoto. Sei'an City is almost certainly intended to be Heian Kyo, as it is in the same location and serves as the capital of Japan (An honor which Kyoto held up until the Meiji Restoration). Like Heian Kyo, Sei'an City is also rectangular. It is likely, too, that Sei'an City's Goyo bridge is a reference to Kyoto's Gojo Bridge. According to legend the warrior monk Benkei stationed himself on the Gojo Bridge and challenged travelers to combat so that he may gain 1,000 swords. Okami obviously possesses an almost exact parallel to this situation.
- The initial graffiti found around the city is the design that Amaterasu drew on her mask in Moon Cave.
- Although the same four people queue in the line outside of Rao's lecture hall, their position changes from time to time.
- The girl drawing with charcoal makes several references to Viewtiful Joe. She will ask you to draw a "V", something she refers to as the "Henshin Pattern". Drawing it successfully will cause her to say "Look, doggy! Isn't it viewtiful? This is my latest design, the "henshin" pattern! Women often want transformation. ...Into real beauties! Henshin-a-go-go, baby!"
- According to Gen's Clock Tower the daytime starts at 5:00 am and night time starts at 9:47 pm