G Project - Panel lining! An easy yet effective way to give your models that extra bit of flair. Here are some of the more common options: 1) Panel-lining Gundam Marker (スミいれ用)-
Amazon.com: GSI Creos Gundam Marker Value Set -GM01&02&03- (Black, Gray, Brown) : Tools & Home Improvement
Gundam Marker Pen Gm01 | Gundam Marker Brown | Gundam Marker Black - Paint By Number Pens & Brushes - Aliexpress
Mr. Hobby Gundam Marker – Lil Thingamajigs Hive
MR HOBBY GUNDAM MARKER BLACK GM01 - CMMODELLISMO
GM02 GUNDAM GRAY FINE LINE MARKER | MasterGrade Hobbies
Gundam Marker GM01 Black Fine Line - Entertainment Earth
Mr.HOBBY Creos GUNDAM MARKER 33 COLOR SET GM01-GM410 | eBay