I Transmigrated and Became a Horse

One-line summary:

A white deer who has practiced for a thousand years should have ascended to immortality, but on her way to repay a debt of gratitude, she accidentally steps onto the path of animal rebirth and reincarnates as a horse! What is she supposed to do?!

Additional summary:

A thousand years ago, an elderly couple helped her transform into human form. They were kind and gentle, but fate had left them childless. She decides to enter the cycle of reincarnation as an immortal and change their fate, so that they can enjoy happiness and fulfillment in their next life.

But something goes wrong during reincarnation. Instead of being born as a human, she becomes a horse. How can she repay their kindness now?

Luckily, by a twist of fate, the white deer still ends up beside her benefactor in this lifetime. Not only does she manage to repay her debt, but together with her big black horse of a brother, a bit of a goof but unbelievably strong and devoted to his little sister, she leads the herd from the mountains to the military camp. She finds comrades and family, experiences a different kind of horse life, and leaves behind a legendary tale of a white horse and black armor in the human world.

In the end, her parents and siblings, everything, become just as she had first imagined.

This story is also known as Happy Little Horse's Ancient-Era Daily Life, The White Horse's Three Lives and Three Worlds, Little White Horse's Slacking-Off Diary, and more...

Things to love:

A white horse who understands human speech, has a quirky mind, is always making snarky comments and causing mischief, and enjoys a cheerful daily life

A super-strong big black horse brother who dotes on his little sister

Funny daily life with other horses, each with their own distinct personalities

Potential deal-breakers:

The horses join human society and go to war. Although the protagonist changes human attitudes so the herd can become true comrades, there is no slaughtering horses for meat, enslaving horses, or whipping them. If you can't accept this premise, please think carefully before reading.

Theme: Stay kind as you grow, then become brave and strong.