This page outlines Ikaruga's relationship with characters in the Senran Kagura 3DS 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.
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's 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. The same case happened during the events of Deep Crimson, except it happened after she witnessed Murasame trying to get Hien back from Ikaruga once again.
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.