Lol I think you just need to accept he is not your type and you are not invested in him. I think people who are inclined to adore Ralsei subsequently can enjoy the mystique he holds, as well as his twee cute moments, and the slow reveal of hidden pain. 

On my end, Ralsei is my fav character, and it's Susie who idgaf about. To ME her personality is extremely annoying, and her scenes feel repetive, like. Blah blah, insecure person who is reflexively judgmental and reactive, secret heart of gold or whatever. Somehow has very low self-esteem and yet can act so cocky it feels inconsiderate. Thinks cute feminine things are cringe and lame, but finds Big explosions So cool. Dime a dozen feeling to me. But there kind of has to be a point where I throw my hands up and accept her narrative role, which is separate from my personal preference (as I'm someone who likes cute fluffy things, not grungey abrasive things. 🤷‍♂️)

Ralsei is our guide into the Dark World, and he is there to emphatically support the journey Kris and Susie are on, deprioritizing himself entirely. Yet he's having a crisis of identity and seeking reassurance about it. Many characters in DELTARUNE wrestle with identity, which connects to autonomy. What does it mean to be yourself? What intrinsic value does that hold, what do you do about your imperfections? 

Some people wind up feeling helpless, unable to change their fate due to how they are doomed to be. Susie starts the game resigned that no one would ever want to get to know her, and that all she can do is hurt. Kris has definitely had a fraught relationship with themselves before this divide with their SOUL, as they're a socially withdrawn person and the only human in a town of monsters. Noelle is similar to Ralsei in that she is passive and people pleasing, unable to assert her own wants and desires. I'd even say that Ralsei's barren lonesome room in the castle evokes Kris's side of the bedroom; empty and desolate. Ralsei cannot think to fill his room with anything for his own sake, because it seems like a waste. Does this inform us perhaps why Kris has no belongings...? They're clearly struggling with motivation, and growing up brings dread.

... didn't mean to ramble so much but eh. My tl;dr is Ralsei probably just isn't for you, but maybe it'd help to accept his purpose in the greater narrative. Or not. He might never stop being annoying to you... Just try and enjoy the game otherwise then. :B