A plot could involve Ruby getting a special power-up related to Unlimited Blade Works. For example, she could gain the ability to project multiple versions of her scythe, like how some characters in Unlimited Blade Works project their weapons. This new power would change the way she fights and she would have to train to master it while also dealing with the threats in her RWBY world that are now more dangerous with this new ability.
Perhaps in the fanfiction, there is a crossover event where the Unlimited Blade Works reality starts to merge with the RWBY world. Ruby is at the center of this, as she is the main character. She has to figure out how to stop the merge from causing chaos. Along the way, she discovers secrets about her own powers and the origins of the two worlds, and forms new relationships with characters from both RWBY and Unlimited Blade Works.
In such a fanfiction, Shirou Emiya could be an ally. He has experience in Unlimited Blade Works and his skills in swordsmanship could complement Ruby's scythe - fighting style. They could learn from each other and fight side by side against common enemies.
Maybe a plot where Ruby discovers a hidden part of her family's past that links her to the Scarlet Spider in some way. This could lead to her having to learn new abilities or face a moral dilemma as she gets involved with the Scarlet Spider's more gritty and morally ambiguous world compared to the more straightforward good - vs - evil of RWBY.
Well, in some fanfictions, a male Ruby might be from a different background than the original Ruby. This could lead to an interesting dynamic with Weiss. For example, he could be from a more noble family, which causes some initial friction with Weiss, who is also from a noble background. As they work through their differences, a White Rose relationship begins to develop. It could involve them facing off against a new type of Grimm that only male Ruby's special skills can help defeat, bringing them closer together.
A third plot idea is that they participate in a tournament together. They have to compete against other teams from different academies. During the tournament, they face some tough opponents who target their weaknesses. Ruby and Blake have to train hard together to overcome these challenges. In the process, they learn new techniques from each other and their relationship evolves from just being teammates to being really close friends who trust each other completely.
Maybe the spider bite is venomous, and Ruby has to struggle with her health deteriorating. As she battles this, she discovers that the venom has a connection to an ancient Grimm or some other dark force. She then has to go on a journey to find the antidote, which might be hidden in a dangerous and unknown place. Along the way, she might meet new allies who have had similar experiences with the spider - related things. And these new allies could teach her how to better manage her situation until she can be fully cured.
Well, one plot could be that Ruby's mother faked her death and is actually alive in hiding. Ruby discovers some clues that lead her to believe this and goes on a journey to find her mother. Along the way, she has to face various challenges and enemies who are also after her mother for their own reasons.
One plot idea could be that Ruby discovers a hidden connection between her Silver - eyed powers and Ozma's ancient magic. Maybe she has visions that lead her to an old relic related to Ozma. Another could be that they team up to fight a new, powerful Grimm threat that is immune to normal Huntsman attacks, but Ruby's unique abilities combined with Ozma's knowledge can defeat it.
One plot idea could be Ruby and Winter teaming up for a special mission. Maybe they have to infiltrate an enemy stronghold. Ruby's speed and Crescent Rose could be combined with Winter's ice powers and combat skills for some epic fight scenes.
One plot idea could be Qrow training Ruby in some special combat techniques that are unique to his own fighting style. This would allow Ruby to gain new skills and also strengthen their bond as family members.
One idea could be Ruby trying to understand Salem's motives beyond just destruction. Maybe she discovers that Salem has a tragic past that led her to this path and Ruby attempts to find a way to redeem her. Another plot could involve Salem targeting Ruby specifically because of her silver - eyed powers and Ruby having to outwit Salem in a series of battles.