I might offer a few helpful tips here. Reiki is already universal energy. Seichim and Reiki are linked but separate systems. Reiki, I have found, is best used as an entirely positive and healing energy. I experimented using it to power other things like sigils and or spells but found it lacking. Usui Reiki is what I would consider pure Reiki and there is a lot of value in focusing on that, particularly for Chakra work.
Seichim on the other hand is what some refer to as Reiki Magick. Most modern Reiki and even Karuna fall way more into this category for me. In Khemitic lineage Seichim or SKHM is one side of the spiritual coin. Heka is more directly linked with Magick and SKHM is linked to the spirit. In fact a way of communicating and directing spirits. This is actually a bit hard to confirm with research currently as so much is behind a paywall. I have been working with Anpu to try and suss more of it out as he is both a master of Heka and Seichim. In any case if you are choosing to use Reiki as a means to power your spellwork or things of that nature I would heavily suggest going this route. Leave Usui purely for what it was originally intended for.
This is not a Karmic scolding or any of that nonsense. This is something I dabbled with personally and have noticed tremendous difference. After my initial experiments trying to use the universal energy as a battery I needed to be attuned again. Like I broke my connection. Seichim however has been an incredible umbrella system. It’s much more favorable for self initiating (though I would suggest finding someone that can attune you to this as well). It’s my personal belief that you can self initiate but it will require much more work and cyclical.