if rizal becomes a bsd character, he'd make a significant role. 1: he could have been working at the seventh agency as a spy for some organization (it is implied in his books—noli me tangere and el filibusterismo that rizal himself hated corrupt officials)

2: he could be an ally of ada because crisostomo ibarra, rizal's reflection of himself in the book noli me tangere, is an erehe (ppl who oppose the catholic faith's beliefs)

i know these two had no connection at all but he could be hawthorne's rival and hawthorne's w fyodor so..

3: rizal is a genius. dazai is a genius.. aside from that rizal had atleast 12 girls in his life before he died. the last one was josephine bracken, his wife. and ik we're all aware that bsd dazai somehow had his collection of girls

4: regarding his ability, he could be someone who can change their identity and perhaps alter memories too. whenever he's at the seventh agency, he uses his persona 'simoun', who is fierce, dark, intelligent, and mysterious.

but the interesting side of his character is

4.1: whenever he's around ada he is ibarra and he possess the same attitude as simoun but ibarra is the softer and playful side of him. and apparently rizal also wants to obtain the book to resurrect the love of his life—leonor rivera.

in the novel noli me tangere+

ibarra and maria clara, who is leonor's reflection, were inlove but they were separated from each other and in the 2nd novel, el fili, ibarra who aimed for revenge with his new identity as simoun, thought maria clara died and that explains as to why bsd rizal wants the book

plus no one knows about his real identity because he has his ability activated all the time, except for yosano. rizal was a surgeon before he infiltrated the seventh agency and he holds yosano's ability in high regards... so the latter knows his real name which is RIZAL.

addendum: irl jose rizal wanted peace and freedom from the spanish colonizers so expect that in bsd universe he'd also do everything to keep yokohama in order