I tested it in the simulacrum, and while it's true that the glaive detonation is a heavy attack and does not proc tennokai, the glaive physically connecting with a target does proc tennokai. Additional bounces after the first hit does not seem to count (at least not with Discipline's Merit).

Using Discipline's Merit, I successfully proced tennokai on every 4 direct (throw) hits with a glaive, resulting in a free glaive detonation through tennokai.

This is tested with Xoris and Wolf's Sledge with various combinations of tennokai mods and levels of glaive bounce.

Edit: I also tested if the extra hit from melee duplicate counts towards Discipline's Merit's 4-hit proc, and with 100% crit chance and a rank 1 (40% chance) Melee Duplicate, I have yet to proc tennokai in less than 4 hits.

The glaive throw is itself a heavy attack. Only normal attacks proc tennokai. So unless you actually attack with your glaive its pointless.

Alright, I had a few tennokai but I didn't know if it's from accidentally melee or thrown. So I did some training test and nothing came up. Forgot to melee to check.

Thanks again

Just as an added note on Tennokai procs; the aerial throw from Cobra and Crane counts, and you can throw the shield and ground slam with the same input and it counts as 2 melee attacks.

I run Opportunity's Reach on mine for giggles and it 100% procs from THROWS, not detonations.