The Godly Siblings of Moon and Sun. Tsukuyomi is a wolf, Amaterasu a fox.
Tsukuyomi is a ruthless fighting nature, who trusts few people and does not play around. He is proud and slightly arrogant to his foes, but friendly to his friends. Few see him in other states than extreme seriosity.
Amaterasu is the exact opposite of her brother in many ways: she is kind- and open-hearted, trusts people relatively quickly (without being naive though) and rarely tries to hide her emotions, which mainly are happiness. If it gets to a battle she gets serious though, and looks much like her brother.
Both Tsukuyomi and Amaterasu are extremely resistant to damage, actually they can not be damaged by anyone save a God, since they are gods themselves. They are not very resiliant to damage among gods though, as their main skills lie in speed, agility, and offensive power. Both Tsukuyomi and Amaterasu have powerful weapons (Tsukuyomi uses a freezing sword known as Kuton, Amaterasu has a mirroir that works like a shield, a sword that allows her to control lightning, and beads that form to a very long chain with which she strikes foes) and abilities as Gods (Tsukuyomi controls the moon, the night, and has overall great powers, Amaterasu controls the Sun, the day, and has special drawing powers which she uses by drawing stuff into the air with her tail. Both can transform into humans as well, in which case they are known as Oki and Sakuya, and have summoning powers which allow them to summon up to an army of 100.000 monsters ready for battle)
Both Tsukuyomi and Amaterasu were young Gods when the Great Snake Orochi striked the land of Nippon, where they lived. Amaterasu's powers got lost as she battled Orochi, making her become nothing but a spirit between the living and dead world, while Tsukuyomi was killed. Amaterasu got resurrected in the body of a simple wolf 100 years later, when Orochi seemed to have come back after having been sealed by Amaterasu's power. Under the name of Shiranui, Amaterasu then searched on Nippon to recover her powers one after the other, and eventually managed to defeat Orochi and the four other Monsters that harassed the world alongside him, under the command of a dark half-deity named Yami: Pest, Shinu Ninetails, Lechku and Nechku. After that she also killed Yami, who had descended to Nippon in a ship known as the Ark of Yamato along with many demons. He had used these demons as well as the five great Monsters to attack the Gods in Heaven, and killed them as they had tried to flee in the ark of Yamato. However, as he died Amaterasu recovered her powers, and her seemingly dead brother Tsukuyomi, who had been reincarnated in a human who had helped Amaterasu during her journey, also recovered his deity state.
Since then Tsukuyomi and Amaterasu have become much stronger to fend off any attacks that might happen in the future just like Yami's, and protect Nippon with all their might, while remaining either a harmless wolf and fox, or friendly siblings to the people of Nippon.