Okina is also the first to be both the final boss and extra boss in the same game, and third boss overall to be a [1-6] stage boss and the Extra stage boss in the same game after Rika and Alice.
Junko doesn't count, since she's at best the Extra stage co-boss and probably more like the Extra stage helper monkey, and Kanako is the Extra stage mid-boss.
Incidentally, Okina joins Alice(5/12.3), Suwako(10/12.3) and Mokou(8/14.5) as the only members of the Extra And Final Boss Club.
Okina is also the first to be both the final boss and extra boss in the same game, and third boss overall to be a [1-6] stage boss and the Extra stage boss in the same game after Rika and Alice.
Junko doesn't count, since she's at best the Extra stage co-boss and probably more like the Extra stage helper monkey, and Kanako is the Extra stage mid-boss.
Incidentally, Okina joins Alice(5/12.3), Suwako(10/12.3) and Mokou(8/14.5) as the only members of the Extra And Final Boss Club.
And also she's the fourth character to be the boss of any two different stages in the same game, alongside Rika, Alice, and Yuuka. But also first to do so in a Windows game. Of course, that's excluding Junko by the same explanation you used.