It has been a long time since I’ve played SH1. I believe amount you save only affects the star ranking. Endings are dependant on tasks you do in the game. You should be alright if you’re saving a lot.

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The number of saves only affects your rank on the results screen. It doesn’t affect the endings.

A lot of older games have great manuals detailing everything.

Doesn’t SH1 say this in the manual?

You need to finish without saving to unlock the secret goth gf, tho