Kaja is a fighter/support hero that deals high magic damage which is one of the reasons why he is META. In the patch before the current one, Kaja's HP was lowered in order to try to balance him. But that only falls popularity out of Kaja so because of that, they adjusted him again. Read this guide until the end to learn more.
Kaja - Lightning Bomb: Removed the short movement speed boost after moving. Reduced the movement speed.
Wrath Sanction: The Basic Damage of the enhanced basic attack increased by 50. The extra damage now is equal to 6% of the target's max HP instead of 5%.
In other words, his passive now deals more damage and his second skill has no speed boosts anymore.
How will this affect the META?
In standard laning, Kaja will be with a marksman and the opposing lane will be an offlaner. Even if the opposing hero is a lane bully, a Kaja and a marksman with red buff will scare it away.
Speaking of red buff, Kaja given this higher damage means he can help the marksman to kill the red buff and rotate faster.
Stealing the gold crab won't be difficult too because of this adjustment.
About his skill 2, it doesn't affect his skill combo that much. It is because the blink distance is enough to pull an enemy towards the team. Kaja need not to use skill 2 to go through the backline if he has the Flicker Spell.
Overall, this is a very good buff for Kaja
Is there a need to adjust my items and emblem configuration?
Generally, no need. Unless you are using Kaja's second skill as a escape skill or really as a way to push through the enemy backline, then here are some things you can do to compensate for the movement speed nerf.
1. If you are not still giving 3 pts for movement speed in your emblem configuration, do it now.
2. Rapid Boots is not good because it has a side effect that once Kaja takes damage, he will be slowed. Rely on Shadow Mask plus another boots instead.
3. There are also items that give movement speed and magic power at the same time. One of the best example is Ice Queen Wand. Also, there are defense items like Brute Force Breastplate wherein once you've use your second skill, your movement speed will be boosted!
How's your Win Rate in Kaja after the new patch? I'm sure that you are doing great already because of this adjustment. If not, I hope this guide helps you.

Kaja - Lightning Bomb: Removed the short movement speed boost after moving. Reduced the movement speed.
Wrath Sanction: The Basic Damage of the enhanced basic attack increased by 50. The extra damage now is equal to 6% of the target's max HP instead of 5%.

In other words, his passive now deals more damage and his second skill has no speed boosts anymore.
How will this affect the META?
In standard laning, Kaja will be with a marksman and the opposing lane will be an offlaner. Even if the opposing hero is a lane bully, a Kaja and a marksman with red buff will scare it away.
Speaking of red buff, Kaja given this higher damage means he can help the marksman to kill the red buff and rotate faster.
Stealing the gold crab won't be difficult too because of this adjustment.
About his skill 2, it doesn't affect his skill combo that much. It is because the blink distance is enough to pull an enemy towards the team. Kaja need not to use skill 2 to go through the backline if he has the Flicker Spell.
Overall, this is a very good buff for Kaja

Is there a need to adjust my items and emblem configuration?
Generally, no need. Unless you are using Kaja's second skill as a escape skill or really as a way to push through the enemy backline, then here are some things you can do to compensate for the movement speed nerf.
1. If you are not still giving 3 pts for movement speed in your emblem configuration, do it now.
2. Rapid Boots is not good because it has a side effect that once Kaja takes damage, he will be slowed. Rely on Shadow Mask plus another boots instead.
3. There are also items that give movement speed and magic power at the same time. One of the best example is Ice Queen Wand. Also, there are defense items like Brute Force Breastplate wherein once you've use your second skill, your movement speed will be boosted!
How's your Win Rate in Kaja after the new patch? I'm sure that you are doing great already because of this adjustment. If not, I hope this guide helps you.