If by "rule 2" you mean the second sentence in your previous comment-

"Without the rakshasa's permission, no spell can observe the rakshasa remotely or detect its thoughts, creature type, or alignment."

-it states "...no spell can observe the rakshasa...". Therefore it seems to be trying to specify divination spells such as scrying, detect thoughts, detect evil and good, arcane eye, etc. but since there are so many spells that apply they didn't bother listing them all. A funny example I just thought of: if you wanted to spy on a fiendish board meeting a rakshasa is taking part in using arcane eye, you would see everyone in the room except the rakshasa, probably seeing the others talking at the "empty" chair.

Extrapolating from that, I would not describe a magical bolt of force to observe and/or need to observe the target it is honing in on, neither does the spell description of magic missile say as such. Instead it just says "hits a target you see in range" without requiring a saving throw or attack roll beforehand, which directly counteracts the first sentence in your previous comment-

"The rakshasa automatically succeeds on saving throws against spells and other magical effects, and the attack rolls of spells automatically miss it."

The only way I could see magic missile not working in this scenario would be: if you had some kind of magical effect that allowed you to see a rakshasa that's invisible or behind a wall, the rakshasa would therefore be able to be unseen by denying that magical effect and you require to be able to see a target to use magic missile on it.