Energy Absorption: Ryan's power. It allows him to absorb pretty much anything energy-based. Also counts as...
Elemental Absorption: Since he is capable of absorbing things like fire, lightning and danmaku bullets.
Actually, lightning is the number-one thing Ryan wants to avoid. As a Mega Man expy of sorts, he is weak to electricity like the classic Mega Man himself—specifically, his muscles seize up, inducing paralysis. Subverted in the case of danmaku bullets, as they still cause pain regardless of absorption.
Sparky is a good boy come the struggle against Flandre in the SDM's basement.
Failed a Spot Check: During Marisa's battle against Cirno, she begins shooting off repeated Master Sparks. She stops firing after a while to take a breather, but finds out that the one tree that wasn't blown up was where Cirno was hiding.
Fake Ultimate Hero: After his quote-unquote "defeat" of FlandreScarlet, Ryan's rocking quite the ego high for a while into the second story arc. The apparent safeguarding of Utsuho he recieves, combined with being sent to settle an incident just gives him an even bigger head. Then Iza shows up, and Utsuho delivers the mortal blow that brings this self-image he has crashing down: Yukari didn't send him to protect Utsuho. She sent Utsuho to protect him. In fact, Utsuho has won virtually every fight for them until that point, with little in the means of effectual help from the supposed "leader". He does not take it well.
When Utsuho breaks it to Ryan that he was never meant to protect her, that she was basically a youkai bodyguard for a weak human even though she was the enemy's prior target, he gets a serious moment of this—complete with regret, self-loathing and questioning of purpose.
Hong Kong Dub: In-universe, due to messing around by Yukari so the English-speaking Ryan and Japanese-speaking Gensokyo residents can understand each other.
Ryan's thoughts: You know, I like this, I really do. These two have been real accommodating, and are very friendly overall. Already, the idea of living in Gensokyo is appealing to me, even Common Sense is giving the thumbs-up! Although I should probably find some bros…waitaminute. Something Reimu mentioned is coming back.
Ryan: Ah... Marisa...?
Marisa: Hm? What's the matter with you?
Ryan: Reimu did say before, after we were working... something about the guy-girl ratio in Gensokyo?
Marisa: Ha! Yeah, you're totally an endangered species, ze. *Ryan headdesks* Hey, at least you've plenty of options for shacking up with someone. They'll probably be more willing than you are to get together, considering the limited options. *headdesk* Especially if you're gonna be a fighter. No guys in Spell Card battles till now, ze. *headdesk* Real quick! If you're thinking of getting with a youkai chick, my advice: don't get frisky in the Spring, ze. *headdesk*
Reimu: Marisa, I think you've messed with the poor boy enough. *Ryan starts to sit up* Although, that last one? Really keep it in mind. *headdesk*
Also, Ran. Very, very much Ran. Once upon a time, she was very much loved by the pre-Gensokyo Human Village, and she loved them in kind. Then, Nami and the Sasa Sanctuary forces of that time tried to kill said humans. The resulting asskicking that Ran delivered was so monumental that Yukari Yakumo immediately wanted her as a shikigami.
Plot Parallel: This has an interesting semi-inversion for the two protagonists. True to the "Heaven and Hell" motif, Ryan and Utsuho have personal agendas that work in opposite directions. Ryan is trying to be stronger so he doesn't weigh Utsuho down, refusing to accept human limits to match his youkai partner. Meanwhile, Utsuho is trying to keep a tight lid on her destructive nature so she doesn't both jeopardize their goal or frighten Ryan away—she's having a bit more success than him, however.
Sempai/Kohai: Once Flandre and Utsuho meet, it doesn't take long for the former to start referring to the latter as "Okuu-senpai".
Shout-Out: Ryan's powers make him very comparable to Zero. (The gun and sword combo being reminiscent of the Mega Man Zero titles does NOTHING to help.) This is lampshaded by Yukari, much to Ryan's embarrassment.
Yukari: Dr. Wily does not approve.
The Champion: Ryan has shown shades of trying to be this for Utsuho's sake. Only succeeds once in a blue moon, however. Primarily during his first encounter with Chino, in the knowledge that he'd attempted to assault Utsuho for rejecting his offer to join the villains of the second story arc.
There Was a Door: When told to assist Patchouli in her first appearance in-story, Sakuya attempts to stop time and exit through a window. Remilia stops her and directs her to the door instead.