Race: Human      
Birthday: Unknown   
Eye Color: Green   
Hair Color: Green   
Loyalty: Keroro Platoon   
Rank: None. Assists the Keroro Platoon.   
First Anime Appearance: Episode 13   
First Manga Appearance: Chapter 55     
Koyuki is a foreign kunoichi who falls in love with Natsumi soon after coming to her home in Japan. She finds and rescues a stranded Zeroro and teaches him the ways of the ninja. After becoming a ninja, Zeroro changes his name to Dororo. She trusts Natsumi to teach Koyuki to live a modern life. She often wears a bow to tie back her hair and can instantly become a ninja. She shares a very close bond with Natsumi. Her skills as a civilian and a ninja are exceptionally outstanding and her athletic ability even rivlas that of Natsumi, making her one of the most physically powerful characters of the series. Despite having amazing powers and quite a hard and strict past, Koyuki is very carefree, optimistic, and eccentric for a normal Japanese girl, but believes in what is right and gets along nicely with her friends.    

Keroro is a frog-like alien sent from his home planet on a mission to conquer Earth. But when his cover is blown, his battalion abandons him and he ends up in the home of the Hinata family. There, he's forced to do household chores and sleep in a dark basement that was once supposedly a prison cell haunted by the ghost of an innocent girl. He even spends his free time assembling Gundam model kits. During his stay, Keroro meets up with subordinates who were also stranded during their failed invasion. 
 
(Source: Anime News Network)

A Japanese voice actor. She's also a certified junior and senior high school teacher.

Hirohashi was born in Niigata Prefecture, and her family's home was a Buddhist temple. Because of this, she attended Ryukoku University in Kyoto, a Buddhist university. In the middle of her first year, however, her parents told her that she could do what she liked, even if it wasn't related to Buddhism, so she sought out what she wanted to do. During her second year, she remembered a radio show she used to listen to in middle school and became interested in voice acting, so she started going to the Aoni Coaching School Osaka while attending university at the same time. The radio personality she had listened to in junior high school was a voice actor, which inspired her to become a voice actor herself.

Non-anime roles:
• Mast - Goddess of Victory: Nikke

Formerly worked on English language dubs for Animax Asia, currently residing in Toronto, Canada.

Sergeant Keroro is the Captain of the Space Invasion Forces Special Advance Team of the 58th Planet of the Gamma Storm Cloud System, sent to the planet Pokopen (aka Earth) to collect intelligence for his planet's invasion force. He is also a frog. After his ship crash-lands in the planet earth, he takes shelter in the Hinata household, but the two kids, Fuyuki and Natsume, find him and take away his alien weapons. When his people discover that the Pokopenians are aware of him, Keroro is abandoned - left to fend for himself in this hostile world. But he's not alone - four other pre-invasion agents were are also lurking on Earth. 
 
(Source: Tokyopop) 
 
Includes chapter 6.5.

During a vacation Natsumi is visited by a female alien and male alien who she later gains feelings for from the ocean that makes her the Deep Sea Princess who, along with the rest of the Keroro Platoon, encounter many dangers summoned by a mysterious creature. 
(Source: Wikipedia)

Sergeant Keroro and his four subordinates came from the planet Keron to the Earth to conquer. However, without notice, they began to enjoy the life on the Earth. Keroro was supposed to stay with Hitana to get the chance to conquer the Earth, but he became friend with Hinata's son, Fuyuki. 
Today, as usual, Keroro goes to buy his favorite Gundam plastic model with Fuyuki. On their way home, they find a small shrine, and enter. There, they find a vase, and happens to break it. Since the next day, strange things happen all over the town and people are in panic. Inside the vase, Kiruru, Keron's ancient ultimate weapon was sealed. At the moment, Mirara who holds the secret of the Kiruru appears and informs them of the only method to save the Earth. However... 
(Source: AnimeNfo)

To celebrate the 20th anniversary of the Sgt. Frog (known as Keroro Gunsou in Japan) anime, Bandai Namco Pictures announced the launch of a new animation project and released a special trailer alongside the news release. Despite the announcement being on April Fools' Day, the official Sgt. Frog Twitter account confirmed the news using the hashtag "For real" (#本当). 

(Source: Crunchyroll News, edited)
 
Note: Title and Relations are provisional and will be updated when more info is announced.

Koyuki Azumaya