This page outlines Ikaruga's relationship with characters in the Senran Kagura PlayStation series.
Ikaruga's relationship with her step brother, Murasame, is a shaky one. At the beginning of the series when Ikaruga was adopted into Murasame's family and inherited the family heirloom, Hien, Murasame resented Ikaruga because Hien was supposed to go to him. However, since Murasame lacked the skills to be a shinobi, it went to Ikaruga instead.
Throughout the games, Murasame attempted to get Hien back from Ikaruga by force, but Ikaruga triumphed him everytime. However, by Shinovi Versus, Murasame admitted that he was terrible as a shinobi and told Ikaruga to fulfill his dream for him by becoming a professional shinobi. From that point on, Ikaruga's relationship with Murasame began to improve.
Ikaruga and Asuka seems to have a stable relationship. Asuka looks up to both Ikaruga and Katsuragi as their seniors and older sisters. They don't interact with one another by themselves, but it's implied that Ikaruga likes helping Asuka become a better shinobi as the team's class representative.
Katsuragi is considered Ikaruga's closest friend out of everyone else she has befriended. During the events of Spark! and a flashback sequence during the anime, their relationship was poor at the start, but as they got to know one another and realize how similar they were, they've became close friends to the point of being able to cooperate with one another fluently in battle. They both look after one another and comfort each other in case they need it. In general, Ikaruga is usually the one keeping Katsuragi in check during her shenanigans when it's not Yagyū on some occasions.
Ikaruga and Yagyū seems to have a stable relationship. There isn't much information about their interactions between themselves, but it's implied that both Ikaruga and Yagyū respect one another and their abilities.
Ikaruga and Hibari seems to have a stable relationship. There isn't much information about their interactions between themselves, but it's implied that Hibari looks up to Ikaruga as Ikaruga guides her to becoming a better shinobi.
Homura Crimson Squad
Yomi is considered one of Ikaruga's closest friends. Throughout both arcs in Burst, Yomi resented Ikaruga for being rich. Due to her mindset of thinking that all people that are rich are spoiled, selfish, and ungrateful, which is why at the start, Yomi called Ikaruga "princess". However, during the Hebijo arc, when Yomi found out that Ikaruga was adopted into her step family, she realized how Ikaruga didn't live a happy life, which caused her to start liking Ikaruga as she began to call her by her actual name.
During the events of Shinovi Versus, their improved relationship shows with Yomi giving Ikaruga advice on how to deal with Murakumo having a personal grudge with her and how Yomi will be happy to teach Ikaruga on how to survive on the streets if she were to become homeless.
Gessen Girl's Academy
It's implied that after the events of both Hanzo's and Gessen's story mode in Shinovi Versus. During the Hanzo story mode, Murakumo resented Ikaruga because since she's part of the Phoenix Conglomerate, Murakumo was separated by her step family due to the Great Wolf Conglomerate adopting her for the sake of competition against the Phoenix Conglomerate. During their final battle with one another, Ikaruga explained to Murakumo that instead of focusing on revenge towards her, she should focus on spending more time with Kurokage since he doesn't have that much time left. Murakumo realized that and admitted defeat.
During the Gessen story mode, Ikaruga begs Murakumo to tell her step father from the Great Wolf Conglomerate to stop the urban development project at the slums since that's Yomi's home. However, Murakumo denies the request since it's only fair for the winner to decide on what to do. During their final bout, Murakumo found out that Yomi is the friend Ikaruga was referring to earlier. However, she still denies Ikaruga's request, even though Yomi is Murakumo's childhood friend. After the fight though, Murakumo decided that she will stop the urban development project despite the fact that she won against Ikaruga. During her time fighting Yomi earlier, she realized that despite both of them being good and evil respectively, they're still friends regardless. With that in mind, Murakumo wants to be friends with Ikaruga as well so that the three of them together can develop an even stronger bond.