Well keep in mind that Japan use more than one alphabet:
- Arabic Numerals
The SNES has 64KB of VRAM (where the tiles are stored). It all depends on how much space the programmer dedicates to store the font. The size of the font would also come into play.
Super Puyo Puyo for example uses a different font set for each stage, with each letter taking up 4 (16x16) tiles. So each font set only displays the required characters.
Rockman and Forte goes for the 1 (8x8) tile approach, so it can store all the Hiragana, Katakana, Numbers, and ? ! 。 etc. To save some space, characters like ブ have the " above the tile as seen here: https://gamefaqs.gamespot.com/snes/562644-rockman-and-forte/images/214
I would have to check the VRAM, but I suspect it only uses the required Latin and Kanji characters. So "D" and "r." would be used for "Dr.ワイリー (Dr. Wily)". 出 (Exit) might be one of the Kanjis that is used.
Super Puyo Puyo 2 doesn't store the font set in the VRAM. Instead it transfers the required character that is needed. This way, you aren't hogging up the VRAM, and store more characters.
Hope that helps.