In order to become a champion of Sen'jin, you'll first need to complete The Valiant's Charge. This is similar to the Aspirant quest where you complete dailies to collect marks. You will recieve 4 marks per day and need to gather 25 before you can become a Champion. Once again you will get A Valiant's Field Training and The Grand Melee. Here's a list of the random dailies you may recieve:

1. A Blade Fit For A Champion: Retrieve the Ashwood Brand. First travel to Grizzly Hills and head East to Ashwood Lake (60, 50). There will be a lot of blue Lake Frogs that you need to /kiss. It's important to use your Warts-B-Gone Lip Balm before you kiss them, every time. It may take a bit before the frog turns into the maiden, however, if someone else finds her you can also speak with her to complete the quest. Please remember that you need to actually speak with her and click on the speech bubble in order to receive the weapon.
2. The Edge of Winter: You are to retrieve Winter's Edge and bring it back to your respective quest giver. Lord Everblaze is who you need to kill for the ember. He's in Crystalsong Forest at (50, 74) up on a cliff. After you've retrieved the ember, you need to head out to Howling Fjord. Winter's Breath Lake is North at (42, 20). All you need to do is target the maiden encased in ice and use the ember in your inventory to free her.
3. A Worthy Weapon: Retrieve the Blade of Drak'Mar. First, you need to gather 4 Winter Hyacinths. They are on the North side of the Ironwall Dam in Icecrown. Afterwards, head out to Dragonblight's Drak'Mar Lake (93, 26). Simply use the Winter Hyacinths and the maiden should appear and spawn the blade.

A note about The Grand Melee: Before you start the fight, make sure you have 3 stacks of Defend up! If your opponent attempts to gain distance to break down your defenses, be sure to use Shield Breaker and Charge if possible. Make sure to keep refreshing your Defend buff or you'll find it hard to defeat your enemy.

After you've completed The Valiant's Charge, you will get the quest The Valiant's Challenge. You'll need to visit Squire Danny at the Western Edge of the Tournament Grounds (70, 25) and defeat your opponent. You will then be given the A Champion Rises quest which will award you with 10 Champion Seals and an Argent Gruntling!