A micro fetish is sexual arousal caused by either being small or having a partner who is significantly smaller than oneself. Micro fetish can be related to macro fetish which involves attraction to much larger partners who dwarf the person with the fetish.
More About Micro Fetish
For one whose micro fetish involves being small themselves, it might include fantasies of being smothered or crushed by a larger partner. If the fetish fixates on the idea of a very small partner then the fantasies may include the ability to physically control their partner.