This isn't incest, but focuses on the bond between two siblings. My character, James is missing most of his right arm and his left arm from the elbow down.

Your character struggles with her mental health, and has been diagnosed with depression in the past.

The two support each other the best they can. James by providing cuddles and helping his sister how helping can when she's struggling, and yours helping James where he struggles with physical tasks.

--

"Sis?"

A small voice tried to break through his older sister's thoughts as James padded slowly and carefully into her room before sitting down next to her on her bed.

Reaching across with his left arm, he placed it on her right hand carefully.  At 7 years old, he was sometimes bullied and teased by other children for being different.

For he'd been born without most of his right arm. It stopped about an inch or two from the shoulder, something he'd grown used to over the span of his lifetime. His left arm was missing from the elbow down. Shuffling into her lap, he sat in silence and just cuddled with his big sister as he always did to try and cheer her up.