
Can someone explain how can a name be said differently when written in kanji as opposed to in katakana? I'm still learning

the characters.
Hiragana is a phonetic writing system, which means that each character represents one character syllable.
Katakana was first developed in the 9th century and is used mainly to write borrowed words from other foreign languages. Just like Hiragana, Katakana has a phonetic value, and each character represents one syllable. It is written in the same way and has the same sounds as Hiragana, with each character representing a sound.
Kanji is the oldest and most complex of the three writing systems in Japanese. It is a logographic (marked by a letter, symbol, or sign used to represent an entire word) writing format which means that each character represents one word.

His name is tomoya in kanji. Kanji can have multiple different readings. I’m not sure what kanji his name actually consist of, but tomoya can be written in multiple different ways. 大弥, this means tomoya with the first part being read as tomo and the second part ya. 和也, this can also be read as tomoya with the same split as before. The kanji characters themselves has multiple different meanings and different ways to read them. I would suggest just looking up explanations on google where I’m sure someone has explained it way better than me here

I'll try and give an explanation as well. I'll use the Tomoya stage name vs. real name as my example here. If spoken out loud, Tomoya is Tomoya there is no difference whether it's written in katakana (how it's done for his stage name) or kanji (the actual spelling for his name). What that translator note is referring to is a change in relationship dynamic between Kei and Tomoya.
So, manga is unique because we have art to show us context but we also have the powerful written word of Japanese. The only problem is there's like 3 alphabets in Japan
The Japanese put a lot of meaning into how something is written. For the majority of the series Kei has been calling him Tomoya, but it's been written using katakana to show he's been using Tomoya as in his stage name. This is just another way for the artist to show Kei being impersonal with Tomoya. Kei is speaking with Tomoya the idol in these instances.
This changes when he says Tomoya but it's written in Kanji (which is the spelling that would be considered his actual name). In this instance, he's speaking to Tomoya his lover not Tomoya the idol.
The difference is meaning in this case. Spoken out loud though, it sounds the same.
I think this may have been what you meant by your question but I'm not sure. I hope this made sense I have ADHD so my explanations aren't always clear
Uda is such a slut of drama, it cracks me up everytime
*for drama