Season 5: Fall of Ninjago

preceded by season 4 and suceeded by season 6 The main antagonist is the Ultra Frown and the Realm Smashers are the villains.

Episodes
45. Day of the Frowns

46. Ninja Frown

47. The Realm of Oni and Dragons

48. Return of the Ninja

49. Chima

50. Ninja Chase

51. The Hunt of the Realm Crystal

52. Ninjago is Gone

53. Escape to the Realm of Oni and Dragons

54. A Final Stand

Focus charavcter
Kai because he found the Realm Crystal and escaped to the ROD aka Realm of Oni and Dragons.