Nemuri Midoriya's alias could reflect her illusion-based Quirk and her antagonistic relationship with Deku. Here are several options, categorized by approach:

I. Names Emphasizing Deception and Illusion:

• Nightshade: Evokes a sense of darkness and hidden danger, fitting for a villain who uses illusions.
• Mirage: Directly references the deceptive nature of her Quirk.
• Specter: Suggests a ghostly, intangible presence, mirroring the ephemeral quality of illusions.
• Wraith: Similar to Specter, implying a haunting and elusive figure.
• Illumina: A more subtle approach, using the root of "illusion" but with a slightly more elegant and deceptive feel. It could be presented as a glamorous, misleading facade.
• Shadow Weaver: Highlights her ability to manipulate shadows and create illusions.
• Phantom Weaver: Similar to Shadow Weaver, but with a more ethereal and ghostly connotation.

II. Names Reflecting Her Relationship with Deku:

• Anti-Deku: A blunt and direct name highlighting their opposition. This could be shortened to "Anti" for a more concise and impactful alias.
• Nemesis: A classic villainous name suggesting a powerful rival or arch-enemy.
• Counterpart: A more sophisticated name suggesting a mirror image or opposite of Deku.
• Reversal: A name that hints at her being the opposite of her brother's heroic nature.

III. Names Combining Illusion and Family Ties (More Complex Options):

• Midori's Shadow: A more poetic name that directly links her to her family name while emphasizing her shadowy nature.
• Nemuri's Veil: Uses her given name to create a more personal and mysterious alias, suggesting a hidden identity.
• Illusion Midori: A simple but effective combination of her Quirk and family name.

IV. Names with a Japanese Aesthetic:

Many MHA names have a Japanese feel. Consider these options, keeping in mind that direct translation might not always capture the nuance:

• Yūgen (幽玄): A Japanese word meaning "a profound, mysterious sense of beauty," fitting for a villain who uses illusions to create a sense of wonder and unease.
• Maboroshi (まぼろし): The Japanese word for "illusion" or "phantom."
• Kagemusha (影武者): Meaning "body double" or "shadow warrior," this could be a fitting name for a villain who uses illusions to deceive.

Choosing the Best Name:

The best name will depend on the specific tone and style you want to establish for Nemuri's character. Consider which name best reflects her personality, her Quirk, and her relationship with Deku. A shorter, more impactful name might be better for a more direct and confrontational villain, while a more complex name could suit a more mysterious and manipulative character.