you read the title, I'm planning a high(17th) level campaign, and want to include titans. the're really cool! (I grew up on Godzilla movies okay) and I'm wondering how one would implement titans besides

1. a world ending threat that we have to keep from waking up (Turrasque, kraken, various giant scions)

2. a golden retriever demigod that is just Walmart Hercules (empyran)

also I think a homebrew titan that's-like- not 20 ft tall would be cool. is that to much to ask?

now don't get me wrong, I think titans as dnd Kaiju are cool and fill an important niche, but typecasting them as ONLY Kaiju is distracting from a rich(I'm drowning in lore over here) and oft-overlooked type of monster.

so, anyone have any ideas?

Well there are the primordials sometimes called dawn titans which are basically gods so can appear how ever you like. Otherwise titans are generally speaking giants in dnd lore so  the will always be big but you can use them any way giants are used in stories. For example: 

• A sleeping or imprisoned titan forms a major part of the terrain such as an island or mountain. 
• A  titan has a hidden forge in a volcano where they make legendary items 
•  A titan living in exile on an island looking after giant sheep. 

There are also some general things that work for all really powerful creatures like 

• The spirit of a titan is trapped in an object
• A titan some how gave up or sacrificed its size or power to  take on a more humanoid form. 
• A titan communicates with players magically in a dream or posses an oracle  to communicate 

that kind of thing