since the beginnning of the year 2019 the Season system has been leaked with all four Ninjas that will exist.

Spring = Shira

Hints for Shira:

1. male

2. can not use Nin-Jutsus

3. Sand Ninja

4. Seaven heaven breathing method

Summer = Shizuka

1. female

2. princess

3. engaged

4. Nadeshiko Village

Autumn = Guren

1. female

2. Kekkei Genkai

3. Sound Ninja

4. Camellia

Winter = Chiriku

1. male

2. Land of Fire

3. Twelve Guardian Ninja

4. 30.000.000 head money

in this video u can see it also

https://www.youtube.com/watch?reload=9&v=aeHY2NDZNIs

btw in some other country Yota is also a mysteroius season Ninja for Autumn

some new Ninjas that exist will be first a ninja in 3vs3 to get them till 3 or 4 stars and then later a season ninja to upgrade them to 5 stars