Guide to Required Documents for D-2-1～4 Visa Extension
1. If an extension is required because your stay expires soon
2. If an extension is required for the extra semester
3. If an extension is required to complete your master's/doctor's thesis
4. If an extension is required due to Bachelor’s (D2-2) → Master's (D2-3); Master's (D2-3) → Doctor's (D2-4)