Bardouin Cecil Efurekea is the biological brother of the late king and eldest uncle of Livius. When Livius ascended the throne, he picked up the role as prime minster and shortly after, abandon the post because he hated the feeling of being weighed down. However, later in the series, the real reason Bardouin left the post was because the pain of Sheila's death returned after Livius and him had conquered the world.
Bardouin is also very popular among the ladies. Livius warns Nike to stay away from him, because he was afraid that Nike would fall in love with him. Later, Livius would put him in jail and confines Nike to her room because of a misunderstanding and anger that his uncle had seduced Nike. However, after the misunderstanding cleared up due to Nike's interference, Livius allows him to return to the Sun Kingdom and resume his job as the kingdom's prime minster. His relationship with Livius also improves.
Despite being older than Livius and the ex-prime minster of the Sun Kingdom, Bardouin is very carefree and jovial compare to Livius. In addition, Barduin is charismatic and well-liked by the people of Sun Kingdom espeically by the ladies. On several instances when he speaks to Nike, he becomes serious when it concern his nephew (Livius) or the late Queen (Shelia).
Although their relationship was strained due to Livius succession as King, Bardouin truly cared about Livius and was both shocked and frighten to see how cold and cruel Livius has grown after Shelia's death. He becomes prime minster again, after his relationship with Livius misunderstandings cleared up due to Nike's interferences. Later on, he also helps Livius run the kingdom whenever he wasn't there.
Although the exact nature of the relationship between the two is unclear, flashback showed that Bardouin loved Sheila very much, however Sheila loved Livius's father. Even after Sheila's death, Bardouin still loved her and was pained by the fact that he couldn't protect her.
Due to Nike's interference, his relationship with Livius improves, and for that he is both thankful and grateful towards Nike. He also accepts Livius relationship with Nike, seeing that she truly loves him when Nike rebuke his advances.