I think this is Marika's mother, Ririka (the change in design from LN to anime is quite bizarre, hard to determine)
A pirate herself, before working at the New Okuhama airport. Marika thought her mother as someone that likes to cosplay because of the pirate attire that Ririka has at home
. Ririka is the one that sew her daughter hat and pirate dress. Sometimes Marika calls her mother, and in some occasions, she'll call her "Ririka-san". In vol 6, Marika saves her mother and the yacht club members
Chiaki Kurihara, daughter of Kenjo Kurihara (Captain of Barbarossa Pirate). She calls her father ヒゲ親父 = Big Oyaji?/Big Daddy?/Big Boss
, who is also known as Captain Black Beard. She transferred to Marika's school to warn her about the circumstances of the future of Bentenmaru. In last year PV, she shots a flare gun to the customers at Marika's work place, Lamp Cafe, as they are polices and army that come to get Marika. She hates it when Marika and the other call her 'Chiaki-chan". During her introduction at the class, Marika blushes as she regards Chiaki a "Bijin" (belle), and at one event at the simulator room, Marika trips and Chiaki catches her. Marika said to herself that her heart is beating fast, even though they are both girls.
Nope they is no implied yuri relation in this novel, except the club President and Vice President
Misa Grandwood. The ship doctor. Ririka and Cain call her "The Blood-soaked Doctor". She also acts as consultant to Marika. In vol 2, when Marika speaks humbly in front of Princess Serenity and regards herself as a 'still learning" Captain, Misa is somewhat upset and said that Marika is a good captain to lead the Benten Maru
Cain McDougal. The ship helmsman. He infiltrates Marika's school as her class room teacher and adviser to the yacht club. Together with Misa, they invite Marika to be the new captain, as they pass the news of the death of Gonzaemon to Ririka and Marika. They then drink wine, (Ririka permits Marika as it was a special occasion) He is the first Benten Maru crew to make appearances in vol 1 prologue as Mr Nice Guy in a Nice Suit with a classic pocket watch (as seen in last year PV)
Glewell Serenity. The 7th Imperial Princess of Serenity Royal Family. An acquaintance to Marika's father. Making her appearance in vol 2, she smuggles herself into Benten Maru cargo bay. She seeks their help to search for the Golden Ghost Ship. Marika calls her a "Princess that likes to smuggles herself" because of several occasions
. Her sister also transfers to Marika's school
百眼 = Hyakume = Hundred Eyes. In charge of Information Analysis and Radar of Benten Maru
Schnitzer. He is a Battle Cyborg in charge of ...battle :P. A similar character was in ARIEL, one of Sasamoto Yuuichi's earlier work
Courier. She controls the electrical weaponry of Benten Maru.
三代目 = Sandaime = The Third. His headband is a dead giveaway. He is in charge of Benten Maru's engine.
Ruka. The navigator. She wears black cloak and possesses a crystal ball.
.....In short, they all become younger as compared to their LN counterparts
. And I'm going to keep Marika's character for a while. Nothing grandiose, but still enjoyable, like other main characters from Yuuichi's novel, which are also females.
In vol 1, Marika is the captain only in the epilogue and the prologue. The main story takes place 6 months before the prologue. Volume 1 main story ends with Chiaki's father saving the club members who navigate the Odette II, where Marika is in charge of communication and the yacht club president, Jenny, at the captain's seat.