Now I know the reason why Tinny didn't appear.
I've let Leif and Seliph meet first before seizing Melgen (I humorously rescued Leif and his crew with Fee in hopes of giving them more experience during the Melgen battle)
So I restart Chapter 6 (Good thing I have a backup save), I got to recruit Tinny, but the house with the Star Sword and money can't be opened (It doesn't have the "Visit" option) and the item on the cliff is unobtainable anymore. But it's alright as long as Seliph has his waifu.
Man, I'm such a screw up. sorry lol.