Zastin

Lala's personal bodyguard and the best swordsman on Deviluke. Initially, Zastin disapproves of Rito, deeming him weak and subsequently seeks to test his strength. However, once Rito exclaims his opinion of marriage in self-defense, Zastin is swayed by his words (though not in the way Rito intends) and summarily approves of him, believing he truly understands Lala's feelings. He bares some resemblence to Creed Diskenth from the manga series Black Cat another series by Kentaro Yabuki.

Personality
He is currently working as the assistant chief to Saibai Yuuki the funds he gets for his duties are handed to Lala for her use. Zastin has shown a keen interest in becoming a mangaka, professionally. He has two assistants that work under him, simply known as Maul and Smutts. Zastin's tail is thin and very scorpion-like in appearance.

Despite his skill with the sword, Zastin has a horrible sense of direction, resulting in him getting lost (one of the running gags in To Love-Ru), Rito states he can be a bit dull like when he's braging about his title as assistant chief of a manga artist to his enemy's, easily persuaded and he constantly works with Rito's dad in drawing manga when it's suppose to be his job as a bodyguard. He also seems to have extremely bad luck, where he keeps getting run over by trains and cars.

Gid Lucione Deviluke
Out of everyone in the series Zastin looks up to and respects Gid the most as the King of the planet Deviluke and Emperor of the entire Milky Way Galaxy, he is one of the bodyguards that protect the king's family members and would get mad at anyone if they disrespect any of them, due to having the same last name its possible that he is related to him in a way but this hasn't been confirme.

Lala Satalin Deviluke
As the first born and heir to the Planet Deviluke, Zastin shows respect to Lala but he would get mad at her and causes him trouble if she where to cause any kind of touble and tries to force her to follow orders as a Princess, like when she ran away from to Earth.

Nana Aster Deviluke and Momo Velia Deviluke
As daughters of the King of Deviluke Zastin expects them to follow orders as Princesse's of Deviluke but instead they follow thier sister to Earth which also causes him trouble even after he failed to bring them back.

Rito Yuuki
At first he didn't accept Rito marrying Lala which would lead him to be the heir to the throun of the future King of Deviluke and Emperor to the Galaxy stating it's not a possition for weaklings and battles him so he would step down, however after hearing Rito's speach about how marriage would only work if two people love each other he mistook this as a right that he is the only one suited for Lala, he then accepts Rito's right to marry her.

Afterwards Zastin started showing respect to Rito even started calling him honorificly as Rito-Dono, he accationaly would help Rito out when he is stuck in a difficult situation envolving something from space and would go to great lenghts to protect him (even though he may fail in the process).