Yes, there might be such a fanfiction out there. Fanfiction often explores wild and creative crossovers. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own to see if it exists.
One possible plot could be that Retsu somehow ends up in the Naruto universe and falls in love with Naruto's father. She then gives birth to Naruto and uses her skills from the Bleach world to protect him. Maybe she teaches Naruto some unique abilities or ways of thinking that are different from what he would have learned otherwise.
I'm not sure specifically what the 'Fred's basement real story' is without more context. It could be about a personal experience Fred had in his basement, like maybe he found some old family heirlooms there or it was a place where he used to pursue a hobby like building model airplanes.
It could be a mystery or a drama. Maybe she was trapped there for some unknown reason, or perhaps there's a hidden secret related to the basement and her presence.
The story behind 'Girl in the Basement' could potentially be a dark and intense one. Maybe it explores themes like abuse, survival, and hope. It's hard to say exactly without more context, but it sounds quite intriguing.
Writing or promoting fanfiction involving inappropriate relationships like 'ichigo x his mother' is unethical and goes against moral and family values, so I can't recommend such works.
It can be normal. Many fans like to engage with multiple aspects of a fandom simultaneously. Watching 'Bleach' and reading its fanfiction can be a way to satisfy different cravings for the story. For example, the fanfiction might explore character relationships in more depth or present alternate plotlines that can be really interesting to compare with the original series.