Rachel's weakness is Dark magic, therefore, Sonic can erect a barrier around Rachel to protect her from the Dark magic in the atmosphere around them. (this cant, however, protect her from Dark energy directed at her سے طرف کی an attack)
Reason #2:
The only thing that Sonic can't do, is swim, henceforth, Rachel, being part mermaid, can work with sonic when forced into an aquatic environment.
(once again, please, no hate comments, this is an "opinion article", so i would appreciate it if آپ would keep yur hate تبصرے (if any hate comments, tho i cant see how آپ could have any hate تبصرے with something like this) to your own thoughts. thank آپ very much!)