It's normal not to be a ninja at level 20. Do more side missions, kill more monsters and steal more materials. You should be able to synthesize the following weapons soon.

Money folding knife

Prop-Persian knife

Material LV 1- Saxon dagger

Material LV2- short handle round handle dagger

Material LV3- broken arrow knife

Material lv4 five-finger dagger

Jewelry-Double-edged Short Knife

Attention-Olyhaka knife

Fight back.-chain mail

Equipment protection-King Kong vest

PS Ninja has the skills of two knives, using Luo Yue's martial arts skills. It is easy to say that you can equip two one-handed weapons for a second attack at the same time.