どんなに～てもNo matter how

Both express 'no matter how', but どんなに〜ても is used with qualities or actions, e.g. どんなに忙しくても行きます ('No matter how busy I am, I'll go'), while いくら〜でも is used with amounts or quantities, e.g. いくら頼んでも無理です ('No matter how much you ask, it's impossible').

どんなに〜ても means 'no matter how' and emphasizes that an outcome remains unchanged even under extreme or difficult conditions, e.g. どんなに努力しても勝てない ('No matter how hard I try, I can't win'). On the other hand, どうしても expresses strong intent or inevitability, often meaning 'no matter what' or 'at any cost', e.g. どうしても行きたい ('I want to go no matter what'). It can reflect either persistence or a lack of alternatives.

Both どんなに〜ても and にしても introduce conditions contrary to results, but with different focuses. どんなに〜ても emphasizes an unchanging outcome despite extreme conditions, e.g. どんなに高くても買います ('I'll buy it no matter how expensive it is'), while にしても is used more flexibly to acknowledge a point while suggesting a contrast or reservation, e.g. 行くにしても、今日は無理だ ('Even if I go, today's not possible').

Both にも〜ない and どんなに〜ても deal with limitations, but in different ways. どんなに〜ても focuses on the resilience or constancy of an outcome despite extreme efforts or conditions, e.g. どんなに頑張っても無理だった ('No matter how hard I tried, it was impossible'), while にも〜ない expresses helplessness or inability despite intent, often paired with verbs of volition or emotion, e.g. 寝ようにも寝られない ('I can't sleep even if I try').

Both are similar in that they describe doing something 'incidentally' to another action. かたがた is particularly formal and used especially in writing, e.g. お礼かたがたお伺いしたく存じます ('I hope to visit you, in part to thank you.'), while ついでに is far more casual and can be used for even simple daily expressions, e.g. 買い物のついでに郵便局に寄る 'to stop at the post office while going out shopping'.