Can we know your living conditions in South Korea? Because depending on where you're in the country, the expenses will be different and if you're in Seoul, you're going to need all the money you've got and those that's sent to you because Seoul is one of the most expensive city in the world. Check your expenses and try to maintain a 1 week routine and see if there's any money left before the next aid comes, if you're struggling to make ends meet at that 1 week routine, you probably need to focus on daily expenses first before investing in bitcoin. This advice is purely my opinion so take it with a grain of salt.
100 dollar is for personal use. I can use it to anything I want. I use father's credit card for my expenses.
Anyway if the $100 you receive from your dad is regarded as stipend for you to use for anything personal to you and the needs that your dad never knew of and you won't account for it, you can invest it in bitcoin. It will be a right time for you to buy bitcoin, I mean some fraction of Satoshi amounting to $90-100 to hodl for the next one year in December next year so you can do a check of how much it has increased and if you want to continue hodling based on ATH.
Don't trade it but only hodl in your personal wallet. If you trade it you may lose all at once.
Since you receive such amount every month, you can invest each month for three times till ending of December. DCA with your earning and with the next bull run you will be glad you have utilize your stipend in a worthy investment.