The relationship could develop through shared experiences. For example, if they both get trapped in a strange dimension in the Bleach world. They have to rely on each other to survive. Ichigo could teach Femichigo about his human side, and Femichigo could show Ichigo new ways to use his spiritual power. This mutual exchange would bring them closer together.
Another plot could be that an ancient evil force targets Femichigo because she represents a new and unknown power in the Bleach universe. Ichigo vows to protect her at all costs. Along the way, they discover secrets about their connection that were hidden by the Soul Society, and they have to fight against not only the external threat but also the political intrigue within the Soul Society.
Another way is by introducing a third party that has a vendetta against both of them. This would force Shirosaki and Ichigo to protect each other, not just because it's the right thing to do, but because they are the only ones who understand the threat this third party poses. This common enemy situation can make their bond stronger as they fight side by side and gradually learn to trust each other more.
The relationship can be developed through shared experiences. For example, if they face a difficult battle together, they will start to rely on each other more. This can break down the initial barriers between them. Another way is through communication. If they start to talk about their feelings, fears, and goals, they will understand each other better.
The new addition to their family could also make them more open about their feelings for each other. They might realize how much they truly care for one another while watching their baby grow. This could lead to more affectionate moments between them and a more solid romantic relationship.
Their relationship can be developed through shared experiences. For example, if they are both stranded on an island, they have to work together to survive. This would force them to communicate and understand each other better.
Another way is to put them in a completely new environment, like a different dimension where the rules are different. In this new setting, they have to depend on each other more. Shirosaki might have to use his wild nature to help them adapt, while Ichigo uses his sense of justice to find a way out. Through these interactions, their relationship can grow and change.
Ichigo could start to take more interest in Orihime's hobbies and vice versa. This would show that they are not just a couple who love each other, but also friends who want to know each other better. For instance, if Orihime likes cooking, Ichigo could start to learn cooking from her and they could have some lovely family dinners together.
Fanfiction could also develop their relationship by giving them a common enemy other than the klaxosaurs. Maybe there is a corrupt authority figure within their own organization who is trying to use them for unethical purposes. Zero Two and Ichigo would have to team up to expose this person. During this process, they would have to trust each other, share secrets, and ultimately grow closer as a result.
They need to have shared experiences. It could be battles against common enemies. In these battles, they learn to trust each other with their lives. Also, communication is key. They should have conversations about their goals, dreams, and fears. This way, they can truly understand each other and develop deeper feelings over time.
The relationship can start with respect. Since Zangetsu is a powerful entity, Ichigo would initially respect her strength. As they interact more, like during training sessions, they can start to share personal stories. This sharing can lead to a deeper emotional connection.