Honestly, nailing a unique character for a Danganronpa RP means resisting the template. So many people default to 'Ultimate Detective's Rival' or 'Ultimate Luck but Edgy.' The setting's premise of extreme talent already boxes you in. I think the trick is to twist the SHSL trope sideways. Instead of 'Ultimate Pianist,' what about 'Ultimate Piano Tuner'? Their talent is noticing minute inconsistencies in sound and environment, which feeds perfectly into class trials for picking apart lies, but their personality could be painfully shy, allergic to the spotlight. Their motive for participating could be sheer financial desperation, not some grand tragic backstory.
Also, the killing game's pressure should warp their talent. Maybe that Ultimate Florist starts seeing poison in every bouquet, or the Ultimate Gymnast's flexibility becomes a terrifying asset in a chase. The most memorable ones I've seen had a mundane talent pushed to a horrifying extreme. Last RP I was in, someone played an 'Ultimate Archivist' who was so obsessed with recording the 'true events' of the killing game they ended up fabricating evidence, becoming an unreliable narrator everyone had to work around. That created way more drama than another brooding survivor.