Character Proficiency is a stat that measures the experience that you have gained with a specific character in Dragon Ball Sparking Zero. There are over 180 characters that you will be able to unlock as you progress through the arena fighter and Character Proficiency is the measure of mastery that you have gained with each of them.
There are seven mastery levels per character, and every time you reach a new level, you will receive a notification that your character proficiency has increased. Character Proficiency is, however, not tied to Player Level, which is the measure of your collective EXP across the game.
Here is a guide that goes over everything you need to know about Character Proficiency in Dragon Ball Sparking Zero.
Does Character Proficiency impact gameplay in Dragon Ball Sparking Zero

As mentioned Character Proficiency just shows the mastery that you have achieved on a character in Dragon Ball Sparking Zero. So the system does not affect gameplay much and once you reach Proficiency Levels 1,4, and 7, you will receive rewards from Zen-Oh which include icon titles as well as Zeni.
So if you are thinking that a higher proficiency level will increase the effectiveness of the character that you are using, that will sadly not be the case. Higher proficiency will only unlock cosmetic rewards.
Best ways to increase Character Proficiency in Dragon Ball Sparking Zero
You will be able to drastically increase the Character Proficiency of your favorite characters in Sparking Zero by taking part in the following game modes:
1) Episode Battle
Episode Battle is the main story mission which will also have what-ifs and Sparking Episodes that you will be able to unlock and they provide a great amount of EXP. These missions follow Goku, Vegeta, Gohan, Piccolo, Frieza, and more, so if you like to play these characters these are a great source of Character Proficiency for them.
2) Custom Battle
Custom Battles are the story battles that are player-generated and shared online. You can either make these battles of your own or try some out from the World Library. These are a great source of Character Proficiency.

3) Bonus Battle
Bonus Battles are special Custom battles that are created by the developer team. These will include special effects as well as other match-ups that you can try to earn more Zeni and Character Proficiency.
4) Online And Local Battle
Online and Local Battles will pit you against other players as well as your friends. You will find this mode on the “Battle and Triangle” page, and booting it up will provide you with a good amount of Character Proficiency.
5) World Tournament
World Tournament is another great source of Zeni and Character Proficiency in Dragon Ball Sparking Zero. They have six tournament rulesets and the more you win the greater proficiency you will receive. You can also create your custom tournament and participate there.
6) Team Battles
Team battles will let you boot up a match with five characters and you will be able to level all of their proficiency up in one go.