Javik, the last prothean, could be an unexpected but interesting addition to a harem. His ancient knowledge and different perspective would contrast with the other characters. Jack, with her powerful biotics and troubled past, could also be part of the harem. And EDI, the AI, could bring a whole new level of complexity to the relationships in the harem with her unique nature.
Shepard could be an interesting character to be part of a harem. Their leadership skills and heroic status would make for an interesting dynamic within a harem. Liara T'Soni is also a great candidate. Her knowledge as an asari and her relationship with Shepard in the original games could be expanded upon in a harem scenario. Garrus Vakarian too, with his loyalty and combat skills, could add a different dimension to the harem.
Tali'Zorah is a character that would bring a unique flavor to a harem. Her quarian background and her relationship with the main character in the Mass Effect series can be further explored in a crossover harem fanfiction. Miranda Lawson is another possibility. Her beauty and her role in Cerberus make her an interesting addition. Aria T'Loak, with her powerful and somewhat ruthless nature, could also be an exciting character in the harem.
Shepard from Mass Effect could be a main character. They could lead the XCOM forces in a joint mission against a common enemy. Their leadership skills would be very useful in coordinating the two very different groups.
Liara T'Soni would be a great candidate. She is intelligent and curious, and Naruto's different abilities and his unique personality would likely draw her in. She would be interested in studying his chakra and his ninja techniques.
Master Chief from Halo is an obvious choice. His super - soldier skills and stoic nature would be really interesting to see in the Mass Effect universe. Another one could be Commander Shepard from Mass Effect. Putting Shepard in the middle of a Halo - style conflict would be exciting. And Cortana, the AI from Halo, could also play a major role. Her intelligence and relationship with Master Chief could be explored in new ways when combined with the Mass Effect elements.
Sakura and Liara would make an interesting pair. Sakura, with her medical ninjutsu skills, could collaborate with Liara, who is also very knowledgeable in the medical and scientific fields. They could exchange knowledge about different forms of healing and perhaps even come up with new techniques by combining their respective medical expertise.
An Asari scientist could be a main character. She might be intrigued by the mystery of the abandoned Earth. Her knowledge of biotics and different cultures in the Mass Effect universe could help her in deciphering the secrets of Earth. She could be the one to make the first contact with any remaining humans or discover important artifacts. Also, a Krogan mercenary could be a main character. His brute strength and combat skills would be useful in exploring the dangerous and desolate Earth. He might be in it for the loot or just the thrill of adventure.
One popular theme is the interaction between different species from the Mass Effect universe in the context of a harem. For example, how a human character might interact with asari, turians, etc. Another theme could be the exploration of different cultures within the Mass Effect world through the harem relationships. It often involves elements of adventure and romance combined, as the main character navigates the complex relationships while also dealing with the larger threats in the universe.
One interesting storyline could be about a character forming a unique bond with different species in the Mass Effect universe within the harem setting. For example, they might start with a relationship with an asari, exploring their long lifespan and biotic abilities. Then add a turian into the mix, dealing with the cultural differences and military discipline. Another could be a story where the protagonist has to navigate the political intrigue of the various alien races while maintaining their harem relationships.
A great Mass Effect crossover fanfiction idea could be a crossover with the Stargate universe. The Mass Effect races could discover the Stargate network and start exploring other galaxies through it. There could be conflicts and alliances with the various races in the Stargate universe. Also, a crossover with the Dragon Age series might be interesting. The mages and warriors of Dragon Age could interact with the biotics and soldiers of Mass Effect. They could learn from each other's magic and technology, and perhaps even fight together against a dark force that threatens both universes.
Shepard and Cayde - 6 would be an interesting pair. Shepard is a skilled military leader, and Cayde - 6 is a witty and resourceful Guardian. Their different personalities and combat skills could lead to some great banter and teamwork.
Potential female characters might include Hinata from Naruto. Hinata has always had a soft spot for Naruto and her gentle nature could be an interesting addition to the harem. In Mass Effect, Miranda Lawson could be in the harem. She is a genetically enhanced human with great combat and leadership skills. Also, Jack from Mass Effect could be part of it. Jack is a powerful biotic with a tough exterior but a complex personality. Each of these characters would interact differently with Naruto in the context of the fanfiction.