I figured it was a contract, so some negotiation would be in order. If I knew the Patron in question, then I could agree or not based on that, but I don't even know if this is who it truly is. It could be something completely different, and I don't want to just say "Yeah, I'll do whatever you say, hyuck!"
But I'm loving the flavor, and if I do go Pact of the Blade, a singing shadow axe would be perfect. I'm really thinking it, too, because of the Invocations I could then get that would help a Fighter. Being able to pseudo-Smite at Warlock 5, and having a guaranteed +1 weapon that can also be a bow at Warlock 3. I don't really need Thirsting Blade to attack twice, since I'd be using Green Flame blade most of the time, because that scales with Character level instead of class level. That's good, because I won't be getting a second attack for quite a while. It's the only downside to multi classing.
Hey, in Xanathar's Guide, it says that an option for Warlocks is that they can have a "Binding Mark" that they can either try to hide, if they don't want people to know, or that they can show to prove their relationship with the Patron. It gives some options, most of which are weird, but one of them might be interesting. It says "One of your eyes looks the same as one of your patron's eyes."
Could I have a glowing eye, perhaps the opposite eye the patron has glowing (preferably the right, but I'm not picky)? I'd still have my normal eye, but it would have a soft glow somewhere inside, noticeable if you look into the pupil. I'm not thinking it is noticeable in the daylight, but maybe if it's dim light or dark, you could tell one of my eyes glows softly. It's thematic, and fits since I picked Devil's Sight as an Invocation. Just a thought!